IBM uses mirrors to pretty up XIV arrays

Space reclamation improved too

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IBM has improved the efficiency of its XIV arrays with instant deleted file space reclamation and added long-distance asynchronous mirroring to better protect and distribute XIV data.

IBM is providing snapshot-based asynchronous mirroring alongside the existing synch mirroring. The two asynch mirror sites can be thousands of miles apart. The mirroring can be done at intervals of 20 seconds up to 12 hours and is either automatic, based on user-set schedules, or manually-driven.

The feature comes with no charge and no need for any hardware revisions. It supports a large number of mirrors, up to 15, and a client can mirror either volumes or consistency groups so that an application or other set of data can be kept in synch together. It is also bidirectional, so hosting systems can mirror and be mirrored simultaneously, and support both synchronous and asynchronous mirroring on each system.

Clients' recovery point objectives (RPO) can be different, and independent of their mirroring schedule. IBM blogger Tony Pearson writes: "You can have up to 128 mirror pairs, and each mirror pair can have its own recovery point objective (RPO). For example, a consistency group of mission critical application data might be given an RPO of 30 seconds, but less important data might be given an RPO of 20 minutes.

"This allows the XIV to prioritise packets it sends across the network. As with XIV synchronous mirror, this new asynchronous mirror feature can send the data over either its Fibre Channel ports (via FCIP) or its Ethernet ports."

IBM has also enhanced the XIV's thin provisioning capability, in which volumes are only allocated enough physical capacity for the written data they have instead of their full logical volume allocation. There is now an instant space reclamation facility, whereby supporting applications, such as Symantec’s Veritas Storage Foundation product, can regain unused file system space in thin-provisioned XIV volumes.

Previously, XIV Thin Provisioning provided space reclamation on a non-instant basis, detecting, zeroing out and releasing unused storage back to the general storage pool on a steady, but slower basis. The new instant capability enables third party products to interlock with the XIV system, detecting unused space instantly and automatically, and immediately reassigning it to the general storage pool for reuse.

3PAR has this capability as well and it also involves Symantec.

Symantec and space reclamation

Norbert Funke, Symantec's EMEA product marketing guy, said: “The Thin Reclamation API within Storage Foundation is available for all storage hardware vendors, including 3PAR. This API ensures a ‘communication’ between the host/file system and the physical storage array to make sure that a thin array will stay thin over time.

"Without such a communication path, a thin array would never know that a file got deleted. Only the file system knows. Therefore Storage Foundation can ‘tell’ the storage array to bring back the freed up storage into the free storage pool.

"Symantec developed this API in collaboration with storage hardware partners. [We are] actively working with storage hardware vendors to make thin reclamation technology available to customers. Some storage vendors have announced thin reclamation capable arrays that support Symantec thin reclamation API. We are also actively engaged with other market leading storage hardware vendors who are undergoing thin reclamation API support qualifications testing."

SVC gets zero detection

IBM has also added zero-detection to its SAN Volume Controller (SVC) product, which virtualises block-access storage arrays and presents their logical capacity to host server applications. Version 5.1.0 of the SVC software has moved to a 64-bit base. This has enabled Zero Detection for Space-efficient Vdisks (virtual disks) using a macro.

IBM Master inventor Barry Whyte blogs: "Zero Detection is implemented in two places, first as a way to go from 'thick' to 'thin' or fully-allocated to Space-efficient using Vdisk Mirroring, and secondly to 'keep thin' once you have a Space-efficient Vdisk, by not writing zero blocks even if the using system does. The latter function is only available on the new CF8 hardware as every incoming write to a Space-efficient Vdisk is scanned by the Zero Detect macro."

SVC zero detection and reclamation facilities come with v5.1.0 of the SVC software. The XIV enhancements will be shipped with new systems from November 19, and will be available to existing XIV customers at no additional cost. ®

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