Defrag HP4300 Lefthand

[JordyL]

Hello

Windows 2008 R2, all disks on SAN including 'C' Drive, HP 4300 4 nodes, 10.5 IQ Software

I have been reading yes and no answers on the following

1) Does it make sense to defrag at OS level, since the OS knows nothing about the underlying storage ?

2) Is there a defrag on the Storage sysetm to run or does the P4300 'auto tune' the data

Thank you

P.S. This thread has been moved from Storage Area Networks (SAN) (Small and Medium Business) to HP StoreVirtual Storage / LeftHand.  - HP Forum Moderator

[Emilo]

See pages 152

http://bizsupport1.austin.hp.com/bc/docs/support/SupportManual/c03035314/c03035314.pdf

Self-Healing Storage
As disk capacities continue to increase, the probability of read errors during a disk rebuild goes up as well. SAN/iQ Network RAID includes self-healing capabilities that improve both the reliability and performance of your SAN. The software scrubs every data block on the storage server at least once per month to reduce the risk of persistent read errors. During these scheduled scrubs, if a data block cannot be read, Network RAID retrieves a copy from the SAN and repairs the data block on the storage server.

Network RAID's proactive defragmentation algorithm runs as a background task. This self-healing feature ensures that both the layout of the existing data and new data storage allocations are perpetually optimized for your SAN.

[oikjn]

Page 152 basically says that you should aviod defraging unless required by the OS.  The reason wasn't because of any feature benefit our SAN has but because defraging thin provisioned LUNs risks excessive writes to the SAN which could in turn cause excessive allocation to the LUN causing the LUN to eventaully grow to 100% allocation even if the actual data on the LUN only should consume <10% of the drive.

Side note.  That manual isn't THAT old...  it says there is NO method for the OS to address the issue of de-allocating the drives.  Sure, StoreVirtual doesn't support the method, but there IS a way that other SANs use as part of the SCSI-3 command set called UNMAP.  I really really hope one day we get that feature as if it isn't around for my next refresh I'll probably be forced to go to another vendor who can support that.