This topic provides answers to commonly asked questions about using Block Storage.

What is an enhanced SSD (ESSD)?

An enhanced SSD is an ultra-high performance disk provided by Alibaba Cloud. Enhanced SSDs use 25 GE networks and the remote direct memory access (RDMA) technology to deliver up to 1 million random IOPS with low one-way latency. For more information, see Enhanced SSDs.

What specifications do enhanced SSDs have?

Enhanced SSDs have three specifications based on their maximum performance. For the latest information about enhanced SSD performance, see Enhanced SSDs.

The performance of a storage device is closely related to the capacity of the device. A storage device with larger capacity provides more powerful data processing capabilities. All ESSDs have the same I/O performance per unit capacity. However, the performance of ESSDs increases linearly with its capacity until the maximum performance per disk for that performance level is reached.
Performance level ESSD capacity (GiB) Maximum IOPS Maximum throughput (MB/s)
PL1 20-32,768 50,000 350
PL2 461-32,768 100,000 750
PL3 1,261-32,768 1,000,000 4,000

What are the similarities and differences between enhanced SSDs, standard SSDs, and ultra disks?

  • Similarities: All three categories of disks are based on a distributed Block Storage architecture, provide high reliability and scalability, and support snapshots and data encryption.
  • Differences: Enhanced SSDs have the best performance among the three categories of disks. For more information, see Enhanced SSDs and Block Storage performance.

How is the performance level of an enhanced SSD measured?

The performance level of an enhanced SSD is proportional to its storage capacity. An enhanced SSD that has a larger storage capacity delivers higher performance. Compared with standard SSDs, enhanced SSDs have much better performance. For more information, see Enhanced SSDs.

How do I test the performance of an enhanced SSD and obtain the 1 million IOPS result?

We recommend that you use fio (flexible IO tester) to perform a stress test on an enhanced SSD. For more information, see Test the IOPS performance of an enhanced SSD.

What is the relationship between the storage performance of an enhanced SSD and storage performance of the instance to which the enhanced SSD is attached?

Instance type specifications impact the performance of instance-level storage. The higher specifications an instance type has, the higher IOPS and throughput it delivers.

For example, when you create an instance of the g5se storage optimized instance family with enhanced performance and attach enhanced SSDs to the instance:

  • If the total storage performance of the enhanced SSDs does not exceed the maximum storage performance that the instance type can deliver, the instance delivers the total storage performance of the enhanced SSDs.
  • If the total storage performance of the enhanced SSDs exceeds the maximum storage performance that the instance type can deliver, the storage performance of the instance is limited to the maximum storage performance that the instance type can deliver.

    For example, you create a 16 GiB instance of the ecs.g5se.xlarge instance type that can deliver up to 60,000 IOPS. If you attach an enhanced SSD to the instance and the enhanced SSD has a storage capacity of 2 TiB with a maximum IOPS of 101,800, the maximum IOPS of the instance is 60,000, instead of 101,800.

For information about the performance and specifications of the g5se instance family, see Instance families.

How are enhanced SSDs billed?

Enhanced SSDs support both subscription and pay-as-you-go billing methods. For more information, see the Pricing page.

In which regions and zones are enhanced SSDs available?

Enhanced SSDs are available in the following regions and zones:
  • China (Hangzhou): Zone G, Zone H, and Zone I
  • China (Shanghai): Zone E, Zone F, and Zone G
  • China (Beijing): Zone F, Zone G, and Zone H
  • China (Zhangjiakou-Beijing Winter Olympics): Zone A and Zone B
  • China (Shenzhen): Zone D and Zone E
  • China (Chengdu): Zone A
  • China (Hong Kong): Zone C
  • India (Mumbai): Zone B
  • UK (London): Zone B
  • Australia (Sydney): Zone B

Which instance families can be attached with enhanced SSDs?

Enhanced SSDs can be attached only to instances from the instance families that support 25 GE networks (g6, g5, ic5, c6, c5, r6, r5, and g5se), ECS Bare Metal Instance families (ebmhfg5, ebmc4, ebmg5, ebmgn6v, ebmgn6i, ebmc5s, ebmg5s, ebmr5s, and sccgn6), and enterprise-level heterogeneous computing instance families (vgn5i, gn6i, gn6v, gn5, gn5i, gn4, ga1, f1, and f3). For more information, see Instance families.

What tools can I use to test the performance of Block Storage devices?

For details, see Performance tests on Block Storage.

Why did my instance shut down when I used fio to test the I/O performance of the instance?

You can use fio to test the I/O performance of an instance by testing raw disk partitions or file systems. However, performing this test on raw disk partitions may damage the metadata of the file systems in the raw disk partitions, which prevents you from accessing files in the partitions. This can also cause the instance to shut down. This problem does not occur when you use fio to test the I/O performance of the instance by testing file systems.

What must I consider when I select zones to create disks and then attach the disks to ECS instances?

A pay-as-you-go disk can be attached only to an ECS instance that is in the same zone as the disk.

  • For high-availability applications, we recommend that you create data disks in different zones and attach them to ECS instances.
  • For low-latency applications, we recommend that you create data disks in the same zone as the ECS instances and attach them to the instances.

What are the common operations that can be performed on a disk?

For information about the common operations that you can perform on a disk, see the "Related operations" section in Disk overview.

How do I query the usage and free space of Block Storage devices?

You can log on to an ECS instance to query the usage and free space of Block Storage devices in the instance. You cannot query the usage and free space of Block Storage devices by using the ECS console or by calling ECS API operations.

Can I shrink a disk?

No, you cannot shrink disks. If you want to shrink a disk that you purchased, we recommend that you create a disk of your desired size and attach it to the same instance as the original disk. Then copy the data stored on the original disk to the new disk and release the original disk.

How do I release a subscription disk that has not expired?

Alibaba Cloud subscription data disks cannot be released before they expire. To release a subscription data disk, you must convert it into a pay-as-you-go data disk first. Before you release the resulted pay-as-you-go data disk, ensure that you have backed up all important data stored in it. For more information, see Convert the billing method of a cloud disk and Release a disk.
Note The disks that have been converted from subscription billing to pay-as-you-go billing are billed by hour. Charges for pay-as-you-go data disks stop one hour after the disks are released. After the disk billing method is changed from subscription to pay-as-you-go, the refund amount is displayed in the ECS console. The coupons that have been used are not refundable.

What is I/O optimization? Can I upgrade an existing ECS instance to an I/O optimized instance?

I/O optimization provides better network capabilities and storage performance for instances and disks. For example, you can optimize the storage performance of a standard SSD by attaching it to an I/O optimized instance.

You can call the ModifyInstanceSpec and ModifyPrepayInstanceSpec operations to upgrade your non-I/O optimized instances to I/O optimized instances.

What is the I/O performance of a standard SSD?

For details, see Block Storage performance.

What scenarios are standard SSDs ideal for?

Standard SSDs provide high performance and high reliability. They are ideal for I/O-intensive applications, such as MySQL, SQL Server, Oracle, PostgreSQL, and other small and medium-sized relational databases. They are also ideal for small and medium-sized development and testing environments which require high data reliability.

Can I replace a basic disk with a standard SSD?

No, standard SSDs cannot be used to replace basic disks because standard SSDs use SSDs as the physical storage media.

How do I purchase a standard SSD? What are the pricing options for I/O optimized instances and standard SSDs?

For pricing details, see the Pricing page.

Can I upgrade a standard SSD after I purchase it?

Yes, you can upgrade and scale up your standard SSDs. For more information, see Overview.

Why is an error reported when I attempt to mount the partitions of a standard SSD to an I/O optimized Linux instance?

In the Linux operating system, the mount points for standard SSDs are in the /dev/vd* format, and the mount points for basic disks are in the /dev/xvd* format. If you specify the mount point in the /dev/xvd* format in a command to mount a standard SSD partition, an error is reported. Specify a mount point in the /dev/vd* format in the command to mount a partition of the standard SSD.

What must I be aware of before I add mount information of basic disks or standard SSDs to Linux instances?

To attach a data disk to a Linux instance, you must format and partition the disk. When you perform this operation, note that /dev/xvdb1 is the mount point for a basic disk, and /dev/vdb1 is the mount point for an ultra disk, a standard SSD, or an enhanced SSD. If the information specified in the mount -a command is incorrect, the disk fails to be attached. To avoid this problem, perform the following steps:

  1. Run the fdisk -l command to view information about the data disk.
  2. Check whether the information of the data disk added to /etc/fstab is the same as that in Step 1.
    Note Do not add duplicate mount information because it will cause a system startup failure.
  3. Run the vim command to modify the /etc/fstab file.
  4. Comment out or delete incorrect information and add correct mount information.
  5. Run the mount -a command to check whether the disk is attached.

For more information, see Format a data disk for a Linux instance.

What is a device name (mount point)?

A device name (mount point) is the location of an ECS disk on the disk controller bus. The selected device name matches the disk device number in Linux and matches the disk sequence number in the disk manager in Windows.

What is an independent disk?

An independent disk is a pay-as-you-go data disk that you purchase separately. An independent disk can be attached to or detached from any ECS instance in the same zone as the disk. You must attach an independent disk to an instance and partition and format the disk before you can use it. For more information, see Create a pay-as-you-go disk.

Can I attach one disk to multiple ECS instances at the same time?

No, a disk can be attached only to one ECS instance in the same zone as the disk.

Do I need to partition and format a pay-as-you-go disk after I purchase it and attach it to an ECS instance?

Yes. After you purchase a pay-as-you-go data disk separately, you must attach it to an ECS instance and then partition and format the disk. For more information, see Format a data disk for a Linux instance and Format a data disk for a Windows ECS instance.

Why am I unable to find the data disk that I purchased for a Linux instance?

If you purchase a pay-as-you-go data disk separately, you must attach it to the instance and partition it before you can view and use its storage space. For more information, see Format a data disk for a Linux instance and Attach a data disk.

How many disks can be attached to one ECS instance?

When used as data disks, a maximum of 16 data disks can be attached to one ECS instance.

Why am I unable to find the desired ECS instance when I attempt to attach a disk to it?

Check whether the ECS instance has been released. If no, ensure that it is in the same zone as the disk.

Can I attach a disk to an ECS instance that is in a different zone?

No, a pay-as-you-go disk can be attached only to an ECS instance in the same zone as the disk.

Will data in a data disk be lost when I detach the disk?

  • In Windows, we recommend that you stop all read and write operations on all file systems of the disk to ensure data integrity. Otherwise, the data that is being read or written will be lost.
  • In Linux, you must log on to the ECS instance and run the umount command on the disk. After the command is executed, log on to the ECS console to detach the disk.

Can I detach a system disk?

Yes, you can detach a system disk.

How is a separately purchased pay-as-you-go data disk billed?

A pay-as-you-go data disk is billed by the hour. Note that if your account balance is insufficient, the services of the data disk will be suspended.

I attached a disk that I created separately to an ECS instance. Why is the disk released when the instance is released?

This is because you have configured the disk to be released along with the instance. You can change this configuration in the ECS console or by calling an API operation. For more information, see Release a disk.

Can I attach a separately purchased pay-as-you-go data disk to a subscription instance?

Yes, you can attach a separately purchased pay-as-you-go data disk to a subscription instance.

Can I detach a data disk from a subscription instance?

No, you cannot detach data disks from subscription instances. Data disks expire at the same time as the subscription instances to which they are attached, and are released together with the instances. To release a subscription data disk, convert it into a pay-as-you-go data disk first. Then detach and release the data disk. For information about how to change the billing method of disks, see Convert the billing method of a cloud disk.

I changed the configurations of a disk when I renewed it. Can I convert the billing method of the disk from subscription to pay-as-you-go within the remaining time of the current subscription?

No, you can convert the billing method of the disk from subscription to pay-as-you-go only by changing the configurations of the instance after the current subscription period ends.

When I delete a disk, will its snapshots also be deleted?

If you have enabled the Delete Automatic Snapshots While Releasing Disk feature for the disk, the automatic snapshots of the disk are also deleted when you delete the disk. However, the manual snapshots are retained. You can change this setting at any time. For more information, see Delete automatic snapshots when releasing a disk.

Why are some automatic snapshots on my disk missing?

When the number of snapshots reaches the upper limit, the earliest automatic snapshots are automatically deleted but manual snapshots are not affected.
Note The automatic snapshot policy that is applied to a disk can be executed only after the disk is attached to an instance.

Can I use a snapshot to create an independent disk?

Yes, you can use an existing snapshot to create an independent pay-as-you-go disk. For more information, see Create a disk from a snapshot.

I cannot access the data in a Linux data disk because an error occurred when I attached the disk. What do I do?

Perform the following steps to fix the error for the Linux operating system:
  1. Find the data disk and use one of the following methods to check whether it is attached to the corresponding ECS instance:
    • Perform the check in the ECS console. For more information, see View the monitoring data of a cloud disk.
    • Log on to the instance, and run the fdisk -l command to check whether the data disk partition information is correct. Run the df -h and mount | grep "<devpath>" commands to view the mount information.
  2. Run the cat command to view the /etc/fstab file and check whether you have attached two disks to the same directory.
    • If two disks are attached to the same directory, the second disk will replace the first disk, causing data of the first disk to become inaccessible. Attach the second disk to a different directory.
    • If they are attached to different directories but the mount information shows that they are in the same directory, run the ll command to check whether a connection exists between the two directories. If a connection exists between the two directories, run the mkdir command to create a new directory, and attach one of the disks to the new directory. Then check whether the data can be accessed.

What do I do if data is lost after I restart an ECS Linux instance?

  • Problem description: All data in a directory such as /alidata is lost after you restart an ECS Linux instance.
  • Cause: After you run the df -h command, the command output shows that none of the data disk partitions is mounted to the directory.
  • Solution: This solution uses an I/O-optimized instance as an example. If your ECS instance is a non-I/O optimized instance, enter the device names of the disk partitions in the /dev/xvd*1 format in the mount command.
    1. Run the fdisk -l command to view the data disk partitions that are not mounted.
    2. Run the mount /dev/vdb1 /alidata command to mount the data disk partitions to the preceding directory.
    3. Run the df -h command to check whether the data disk partitions are mounted to the directory.
    4. Optional. Configure the /etc/fstab file for the system to automatically mount the disk partitions during next system startup to avoid this problem.

Are my snapshots retained if I re-initialize a disk?

Yes, both manual and automatic snapshots in the disk are retained.

Data disks of a Linux instance cannot be found after I restarted the instance or re-initialized the system disk. What do I do?

  • Problem description: After you restart a Linux instance or re-initialize the system disk, you log on to the instance and run the df -h command. The command output shows that no data disks are found.
  • Cause:
    • Restarting an instance: Mount information was not written to the /etc/fstab file before you restart the instance. As a result, data disks are not automatically attached after the instance restarts.
    • Re-initializing the system disk: The /etc/fstab file is reset after the system disk is re-initialized. As a result, data disks are not automatically attached during system startup.
  • Solution:
    1. Run the mount /dev/xvdb1 command to remount the data disk partitions.
    2. Run the mount command to check the file system of the /dev/xvdb1 partition.
    3. Assume that the file system of the /dev/xvdb1 partition is ext3. Run the following command to write the partition mount information to the /etc/fstab file:
      echo '/dev/xvdb1 /data ext3 defaults 0 0' >> /etc/fstab
    4. Restart the instance in the ECS console.

How do I reattach data disks after I re-initialize the system disk of a Linux instance?

After you re-initialize the system disk of a Linux instance, data in the data disks that are attached to the instance remains unchanged, but the mount information of the data disks is lost. As a result, all the data disks become detached. Assume that before the system disk is re-initialized, a data disk partition mounted to the instance is named /dev/vdb1, and its mount point is named /InitTest. Perform the following steps to remount the data disk partition after you restart the Linux instance:
  1. Run the mount command to view the mount information of the data disk.

    The command output does not contain information of /dev/vdb1.

  2. Run the fdisk -l command to view information about data disk partitions.
  3. Run the cat /etc/fstab command to view the original mount point name of the /dev/vdb1 data disk partition.
  4. Run the mkdir /InitTest command to recreate the mount point for the data disk partition.

    For the /dev/vdb1 data disk partition, the new mount point name must be the same as the original one.

  5. Run the mount /dev/vdb1 /InitTest command to remount the data disk partition.
  6. Run the df -h command to check whether the data disk partition is mounted.
  7. Perform the following steps to check whether the/dev/vdb1 data disk partition can be automatically mounted:
    1. Run the umount /dev/vdb1 command to unmount the /dev/vdb1 data disk partition.
    2. Run the mount command to check the mount information.

      If the command output does not contain information of /dev/vdb1, the partition is unmounted.

    3. Run the mount -a command to automatically mount /dev/vdb1.
    4. Run the mount command to check the mount information.

      If the command output shows information of /dev/vdb1, the partition is automatically mounted.

Are my snapshots retained if I replace a system disk?

This depends on how the snapshots are created. Manual snapshots are retained, but automatic snapshots are deleted if the Delete Automatic Snapshots While Releasing Disk feature is enabled.

Note After a system disk is replaced, the disk ID changes. You cannot use the snapshots of the original system disk to roll back the new system disk.

What must I be aware of before I replace a system disk?

We recommend that you create snapshots of the current system disk before you replace it. Make sure that the new system disk has enough space available. The recommended available disk space is 1 GiB or larger. If disk space is insufficient, the instance may not start properly after you replace the system disk.

How do I extend a system disk?

You can extend a system disk in the ECS console or by calling the ResizeDisk operation.

Can I shrink a system disk after I extend it?

No, you cannot shrink a system disk after you extend it. We recommend that you extend the system disk reasonably based on your needs.

What Block Storage devices can be extended when they are used as system disks? Do any regional limits apply to this operation?

Ultra disks, standard SSDs, and enhanced SSDs can be extended when they are used as system disks. You can extend system disks in all regions.

Can the system disks of both subscription ECS instances and pay-as-you-go ECS instances be extended?

Yes, the system disks of both subscription ECS instances and pay-as-you-go ECS instances can be extended.

What is the storage capacity range of a system disk?

The capacity range of a system disk varies with the operating system. For more information, see Overview.

I changed the configurations of an instance when I renewed it. Can I specify a new size for the system disk when I replace the system disk?

After you downgrade the configurations of a subscription instance when renewing it, you can extend its system disk only when the new billing cycle starts.

How do I create a disk from a snapshot of a data disk to extend the data disk without risking data loss?

If a data disk cannot be extended without data loss due to a disk error, you can purchase a pay-as-you-go disk to temporarily store data from the original data disk, and then format the original data disk. To do so, perform the following steps:
  1. Create a snapshot of the current data disk (original data disk). For more information, see Create a normal snapshot.
  2. Go to the disk purchase page. Select the region and zone of the ECS instance to purchase a pay-as-you-go disk. Click Create from Snapshot. In the dialog box that appears, select the snapshot created in the previous step.
  3. Log on to the ECS console and then attach the new data disk you purchased in the previous step to the ECS instance.
  4. Log on to the ECS instance and run the mount command to attach the new data disk to the instance. For more information about how to attach a disk created from a snapshot, see Create a disk from a snapshot.
  5. Check whether files in the new data disk are the same as those in the original data disk.
  6. Run the fdisk command to delete the original partition table. Then run commands such as fdisk and mkfs.ext3 to repartition and reformat the new data disk, extending it to the target capacity. For more information, see Resize partitions and file systems of Linux data disks.
  7. Run the cp -R command to copy all the data in the new data disk back to the original data disk.

    You can add the --preserve=all setting to retain the file properties when you copy the files.

  8. Run the umount command to detach the new data disk.
  9. In the ECS console, detach the new data disk from the ECS instance, and release the disk.

What do I do if the "Bad magic number in super-block while trying to open /dev/xvdb1" error message is returned when I extend a disk of a Linux instance?

  • Problem description: When you run the e2fsck -f /dev/xvdb command to extend a disk of a Linux ECS instance, the "Bad magic number in super-block while trying to open /dev/xvdb1" error message is returned.
  • Cause: The disk to be extended is not partitioned.
  • Solution: Run the e2fsck -f /dev/xvdb and resize2fs /dev/xvdb commands to extend the disk. Then run the mount command to attach the disk.

Can I partition a data disk for data storage?

Yes, you can split a data disk into multiple partitions as needed. We recommend that you use the system tool for partitioning.

For a disk with multiple partitions, are snapshots created for the entire disk or only for a specific partition?

Snapshots are created for the entire disk, instead of for a specific partition.

What must I be aware of before I repartition a disk?

To ensure data security, we recommend that you create a snapshot of a disk before repartitioning the disk. This way, you can roll back the disk if you perform an incorrect operation. For more information, see Create a snapshot and Roll back a disk by using a snapshot.

What is the relationship between writing data and partitioning and formatting?

A new disk or disk partition can be used only after it is initialized and has its data structure recorded on the disk. The goal of formatting is to create file systems. Therefore, when a file system is created on a disk, data of the file system is written to the disk. The amount of data written to disks during formatting varies based on the file system.

  • In a Windows instance, you can use one of the following methods to format a data disk:
    • Quick format: This method allows you to allocate only file systems to partitions and rewrite the directory table. Quick format takes up less space.
    • Full format: This method allows you to allocate files systems to partitions, rewrite the directory table, and scan for and mark damaged sectors. In addition, during the formatting process, empty data blocks on the disk are filled in, which is equivalent to writing the entire disk. In this case, the size of the first full snapshot is approximately equal to the disk size.
  • In a Linux instance, if no data is written to a disk after you format the disk, the size of the first snapshot depends on the format of file systems on the disk.

I rolled back a data disk by using a snapshot after I repartitioned the disk. How many partitions are available in the disk?

When you roll back a data disk by using a snapshot, the disk returns to the status it was in when the snapshot was taken. If the disk has not been repartitioned when the snapshot was taken, only one partition is available in the disk.

An error message similar to the following one is returned when I attempt to roll back a disk: "A disk can be rolled back only when the attached instance has been stopped and the disk has no snapshots being created. If the operating system of the current ECS instance has been replaced, the snapshot taken before the replacement cannot be used to roll back the new system disk." What do I do?

  • Problem description: When you attempt to roll back a disk by using a snapshot, an error message similar to the following one is returned: "A disk can be rolled back only when the attached instance has been stopped and the disk has no snapshots being created. If the operating system of the current instance has been replaced, the snapshot taken before the replacement cannot be used to roll back the new system disk."
  • Cause: The problem may be caused by an incorrect disk property or disk state.
  • Solution: You can troubleshoot the problem based on the instance status or snapshot status.
    • Check whether the instance to which the disk is attached has been stopped.

      You can roll back disks only when the instance to which the disks are attached is in the stopped state. You can log on to the ECS console and check the status of the instance on the Instances page.

    • Check whether the system disk of the instance associated with the snapshot has been replaced.

      If you selected a new image to replace the system disk, a new system disk is automatically recreated from the new image and the system disk ID changes. Therefore, you cannot use the snapshots taken for the original system disk to roll back the new system disk. However, you can create a custom image from one of these snapshots and then use the custom image to replace the system disk of the instance. This way, the instance returns to the state it was in when the snapshot was taken. For more information, see Create a custom image from a snapshot and Replace the system disk (non-public images).

    • Check whether the disk to be rolled back has a snapshot being created.

      To ensure data consistency, Alibaba Cloud does not allow users to roll back a disk when a snapshot is being created from the disk. You can go to the Instance Details page. Click Instance Snapshots in the left-side navigation pane. Check the status of snapshots. A snapshot is being created if the Progress value is not 100% and the Status value is Progressing.

      If you need to forcibly terminate the creation process of a snapshot to roll back the disk, select the snapshot and click Delete.

How do I migrate data from the system disk of a Linux instance?

Assume that you purchase an ECS Linux instance without attaching any data disks to it. After the instance is used for a period of time, its system disk usage approaches 100% and can no longer meet your business needs. To solve this problem, you can purchase a data disk and attach it to the instance. Then, run the mv command to migrate data from the system disk to the data disk.

How do I copy data across instances?

You can choose data copy methods based on the operating system:
  • Copy data between Linux instances
    • Use the lrzsz tool

      Log on to the Linux instances, install the lrzsz tool, run the rz command to upload files to one Linux instance, and then run the sz command to download the files to the other Linux instance.

      You can also first run the sz command to download files to your local PC and then run the rz command to upload these files to the other Linux instance.

    • Use the FTP service

      If you use the SFTP tool, we recommend that you use the root account to log on to instances and to upload or download files.

    • Use the wget command

      On one instance, compress a file or a folder and then save it to the web directory to generate a download URL. Then run the wget command on the other Linux instance to download the file or folder.

  • Copy data between a Linux instance and a Windows instance

    We recommend that you use the SFTP tool to download files from the Linux instance to your local PC and then use the FTP service to upload the files to the Windows instance.

  • Copy data between Windows instances
    • Use the FTP service
    • Use TradeManager