making a hot spare ... hot
flat view
From: Brendan Hide <hidden>
Date: 2011-09-21 03:30:17
Hi all To the point: When a disk is designated as a hot spare, would it be of benefit to spread copies of data chunks from the other disks onto the hot spare even before a failure? Has this been tried before? If its not already being done, it'd have a small positive consequence for performance as well as data integrity, with relatively little to no negative consequences. Benefits would diminish the larger the array, much like the performance difference between raid3 and raid5. Read speeds would theoretically increase and write speeds should not decrease except in the case of poor hardware. Given a 6-disk raid5 (5 "data" disks + 1 spare) array, a re-sync will start at 25% progress from the moment a disk gets dropped out of the array. The theoretical max read speed will also increase by 16% by reading from 6 disks instead of 5. The cons will be that, when writing, an extra write will need to occur to the "spare" disk. Though this shouldn't have any performance penalties on modern hardware I can still see it as being a concern. I suspect something like this might have been suggested before - but I haven't been able to find any reference to something along these lines online. I'll welcome any discussion or links to relevant information. Thanks. Key: 0-F: Data Chunks P: Parity Layout of standard RAID5 + 1 standard spare Disk0: 048C Disk1: 159P Disk2: 26PD Disk3: 3PAE Disk4: P7BF Disk5: Spare (empty) Chunks read per read "cycle": 5 Time to read all 16 data chunks: 4 cycles Layout of standard RAID5 + 1 "hot" spare: Disk0: 048C Disk1: 159P Disk2: 26PD Disk3: 3PAE Disk4: P7BF Disk5: 05AF Chunks read per "cycle": 6 Time to read all 16 data chunks: 3 cycles -- __________ Brendan Hide Mobile: brendan.cell@swiftspirit.co.za (plain text only please) Web Africa - Internet Business Solutions http://www.webafrica.co.za/?AFF1E97