Network RAID-5 and 6 question

[Richard v. Laanen]

Hi,

In the new SAN/IQ release (8.5) it's possible to set a volume to network RAID-5 and 6. It will write the blocks to different Storage Nodes and also a parity block is written to a node(in case of RAID-6 two parities are written). When creating a volume with the new RAID levels, a messages is displayed telling that with this RAID levels thin provisioning will be the best choice (and it defaults to that setting). Also a snapshot schedule is automaticly created to snapshot the volume once a day and keep one snapshot alive.

Does anyone knows why this is done?

Thnx ahead, Richard.

[Uwe Zessin]

The snapshot is in a different RAID level -- if I remember correctly, this is for performance reasons - otherwise we'd see the 'RAID-5/6 write penalty'.

[Robert Lennie · Accepted solution]

http://blogs.hp.com/p4000/2010/02/12/network-raid-5-and-6-explained/

Highlights:
Network RAID5 is a Background Parity Based Encoding method that reclaims disk space based on snapshots that are taken. I'll refer to it as PBNR (parity based network raid)
The top level volume is still a Network RAID10 volume, and that is to maintain performance and availability.
PBNR does not run on the top level volume because of the performance impact of the read-modify-write algorithms for small writes
Over time snapshots are merged over time, and most of the data end up in there
The greater the change rate, the less space is 'reclaimed'
Make sure the default schedule that is setup for the snapshots is setup to off peak hours

[Richard v. Laanen]

Robert,

Your answer is very usefull, thanx.

Richard.

[Richard v. Laanen]

The answer of Robert is right on the money.