4 KB Sector Support

Many applications manage large blocks of data—much larger than the legacy hard drive sector size of 512 bytes. Advanced Format Drives (AFDs) consisting of 4 kilobyte (KB) sectors are more efficient with applications that manage large blocks of data. SANsymphony software takes advantage of the benefits of 4 KB sector disks by allowing the creation of disk pools from which virtual disks with 4 KB sectors can be created.

Sector sizes matter when it comes to creating disk pools, virtual disks, and performing operations on virtual disks. This topic provides information about 4 KB sector support and guidelines for using different sector sizes in disk pools and virtual disks.

About 4 KB Sector Support

 Refer to host operating system documentation to verify that hosts support virtual disks with a 4 KB sector size. Virtual disks with a 4 KB sector size are not supported with Windows Server versions prior to 2012. Virtual machines hosted by ESX can use virtual disks with a 4 KB sector size as long as the virtual machines are running an operating system that supports it. An ESX hypervisor itself cannot use virtual disks with a 4 KB sector size to store virtual machine images, snapshots, or configuration data.

Disk Pools

o           The sector size of a pool is selected when the pool is created and cannot be changed. (See Creating Disk Pools.)

o           Only physical disks with 4 KB sectors (including pool mirrors) can be added to pools with a 4 KB sector size. In addition, physical disks with different sector sizes cannot be mixed in any pool.

o           Pools with 4 KB sector size can only be used to create virtual disks with a 4 KB sector size. (Although virtual disks with a 4 KB sector size can be created from pools with either 4 KB or 512 B sector size.)

o           Storage allocation units can be any allowed size.

Virtual Disks

o           The sector size of a virtual disk is selected when the virtual disk is created and cannot be changed. (See Creating Virtual Disks.)

o           Virtual disks with a 4 KB sector size can be created from pools with sector sizes of either 512 B or 4 KB. In addition, mirrored virtual disks with a 4 KB sector size can have one storage source created from a pool with a 4 KB sector size and the other created from a pool with a 512 B sector size. (Virtual disks with a 512 B sector size can only be created from pools with a 512 B sector size, not from pools with a 4 KB sector size.)

o           Virtual disks with a 4 KB sector size, can use a pass-through disk as a storage source if the disk sector size is 4 KB. Sector sizes of pass-through disks must always match the virtual disk sector size.

o           Snapshot is supported. For a virtual disk source with a 4 KB sector size, the snapshot can be created from a pool with a sector size of either 4 KB or 512 B. Mapstore pools may have a sector size of either 4 KB or 512 B, regardless of the sector size. (Virtual disk source with a 512 B sector size can only create snapshots from pools with a 512 B sector size, not from pools with a 4 KB sector size.)

o           Continuous Data Protection (CDP) is supported. For a virtual disk source with a 4 KB sector size, the rollback can be created from a pool with a sector size of either 4 KB or 512 B. The history log may have a sector size of either 4 KB or 512 B, regardless of the virtual disk sector size. (Virtual disk source with a 512 B sector size can only create rollbacks from pools with a 512 B sector size, not from pools with a 4 KB sector size.)

o           The Sequential Storage feature is supported for virtual disks with a 4 KB sector size.

o           Replication is supported. The virtual disk source and destination must have the same sector size.

o           Move and Replace operations are supported. A virtual disk storage source with a 4 KB sector size can be migrated to a pool with a sector size of either 4 KB or 512 B. (Virtual disk storage sources with a sector size of 512 B can only be migrated to pools with 512 B sector size, not to pools with a 4 KB sector size.)

o           Virtual disks can be converted to other types (single, mirrored, or dual), provided that the sector size rules are obeyed.

o           When performing operations with multiple virtual disks (such as Move, Replace, Convert to Mirrored), the sector size of the storage sources being manipulated in the operation must be the same; either all 512 B or all 4 KB.

o           Virtual disks with a 4 KB sector size are not supported for use as VVOLs or protocol endpoints.

o           Data can be migrated from a virtual disk with a 512 B sector size to a virtual disk with a 4 KB sector size by manually copying the data on the host.