Disks
Disks are virtual versions of physical storage devices, such as SSD and HDD.
Disks are designed for storing data and are attached to VMs. Detaching a disk does not delete its data.
Each disk is located in an availability zone, where it is replicated (unless it is a non-replicated disk) to provide data protection. Disks are not replicated to other zones.
Disks as a Nebius Israel resource
Disks are created within folders and inherit their access rights.
Disks take up storage space, which incurs additional fees. For more information, see Pricing for Compute Cloud. You specify the disk size when you create it, and this is the storage capacity you will be charged for.
In case you create a disk from a snapshot or image, its information will contain the ID of its source. The license IDs (product_ids) used to calculate the disk use cost are also inherited from the source.
Disk types
Nebius Israel VMs can use the following disk types:
- Network SSD (
network-ssd): Fast network drive, which is an SSD based network block storage. - Network HDD (
network-hdd): Standard network drive, which is an HDD based network block storage. - Non-replicated SSD (
network-ssd-nonreplicated): Network drive with enhanced performance without redundancy. - High-performance SSD (
network-ssd-io-m3): Network drive with the same performance characteristics asnetwork-ssd-nonreplicated, plus redundancy. High-performance SSDs are currently at the Preview stage.
Network SSDs, high-performance SSDs, and network HDDs provide sufficient redundancy for reliable data storage and enable continuous read and write operations, even when multiple physical disks fail at the same time. Non-replicated disks do not ensure data security.
If a physical disk hosting a network drive fails, the VM will continue running and will quickly regain full access to its data.
Non-replicated disks and high-performance SSDs
Non-replicated disks and high-performance SSDs outperform network SSDs but have the following limitations:
-
Disk size must be a multiple of 93 GB.
In all calculations, 1 GB = 230 bytes.
Alert
Our recommendation is to avoid using a non-replicated disk as your boot drive. This is because, in case it fails, your virtual machine may become unavailable.
If you need enhanced performance and guaranteed fault tolerance, we recommend using high-performance SSDs.
Maximum disk size
Disks consist of blocks. By default, the block size of all created disks is 4 KB; however, this is not enough for disks larger than 8 TB. You can set the block size when creating an empty disk. In this case, you will immediately see the maximum disk size. You cannot change the block size after the disk is created.
The maximum disk size depends on the specified block size. The size of a newly created disk must be a multiple of 4 MB.
| Block size | Maximum disk size |
|---|---|
| 4 KB | 8 TB |
| 8 KB | 16 TB |
| 16 KB | 32 TB |
| 32 KB | 64 TB |
| 64 KB | 128 TB |
| 128 KB | 256 TB |
Alert
The selected physical block size may affect disk performance.
In most cases, the logical block size is equal to 512 bytes. Although the OS tries to align data I/O with the physical block size, this might not always be possible. In case the software performs many read/write operations with a size that is less than the physical block size, such small operations may reach the disk subsystem. When it comes to read operations, this means reading more data than actually requested, i.e., at least one physical block. In case of write operations, the situation is even more complicated, as writing data with a size that is less than the physical block size requires first reading the entire physical block, then modifying the requested bytes, and, finally, rewriting this block (this is known as read-modify-write operation). As long as such an operation is not aligned to the physical block size, it may also be required to read and rewrite as many as two physical blocks. Thus, a single logical write operation may turn into two read and two write operations at the disk subsystem level. This extra load will not reveal itself in the guest OS metrics, but will matter when the load is compared to the disk limits and will eventually affect performance.
This is why we recommend picking large block sizes only in case your software uses large requests (at least equal to the physical block size) when working with the file system or disk.
Attaching and detaching disks
You can only attach each disk to one VM at a time. Additionally, both the disk and the VM must be in the same availability zone.
To successfully boot a VM up, you will need a boot drive. Optionally, you can then attach more disks to your VM.
Note
Empty disks do not have a file system. If you attach an empty disk, partition and mount it manually. Alternatively, instead of attaching an empty disk, you can create a snapshot of the boot disk and create a VM based on such a snapshot.
When selecting a disk to attach to a VM, you can specify that the disk should be deleted once you delete the VM. This option is available when you create a VM, reconfigure it, or attach a new disk to it.
If a VM had any previously created disks attached, they will be detached when you delete the VM. The data on the disk will be still there, and you will be able to attach the disk to a different VM later.
If you would like to delete a disk with a VM, specify this option when creating the VM, reconfiguring it, or attaching the disk. Such disks will be deleted along with the VM.
Backups
Backups are required to make sure no data is lost if damaged. Different disk types allow using different backup methods:
- Cloud Backup enables you to create consistent data copies on VMs with any disk types.
- Disk snapshots: Use them to manually or automatically create scheduled snapshots of network SSDs and HDDs, as well as high-performance and non-replicated SSDs. You can also use snapshots to migrate disks from one availability zone to another.
Snapshots are replicated across all availability zones, which allows you to migrate disks from one zone to another.
Sometimes, you may want to restore a disk to a specific state on a regular basis, for instance, when you need to attach the same boot drive to every new VM. In this case, you can upload a disk image to Compute Cloud, which will allow you to create disks faster than you would do it from snapshots. Images are also automatically replicated to multiple availability zones.
You cannot recover a boot disk of an existing VM from a snapshot or image. However, you can create a new VM to recover a boot disk from a snapshot.
For more information on backing up and restoring VMs, see Backups in Compute Cloud.