Faster Linux Software RAID Rebuilds
This Cyberciti.biz article explains settings and techniques to increase the default RAID re-build performance from 4k to 51k in his example. The key settings were
- Increase the speed limit max by adding dev.raid.speed_limit_max = 500000 to /etc/sysctl.conf
- Enable bitmaps during the rebuild and disable them after
- sudo mdadm —grow —bitmap=internal /dev/md0
- sudo mdadm —grow —bitmap=none /dev/md0
My md-RAID has not had a failure in over a year that forced a rebuild. The only failure I’ve ever seen were a loose SATA cable and if it is caught quickly enough, no rebuild is needed. Usually a rebuild is 4 hours or so.
Array Upgrades
The day is coming when I’ll swap the 320GB drives with 1.5TB drives and need to rebuild the entire array. I wish it was a 5 drive array, so RAID6 would be a viable option without loosing too much usable storage.
Regardless, when I do swap the new drives in, I will limit the assembled RAID partitions to 1TB in size so backups to external eSATA disks for each array are easier. They make 1.5TB disks, they do not make 4.5TB disks … yet. When I’m done, I think I’ll have 4 separate RAID disks to present, (3) 1TB and (1) around 400GB.
Backups to eSATA Disks
Those arrays will need to be backed up somehow. For me, that means external eSATA disks due to cost and convenience. Basically, I don’t want any of the arrays to be larger than a single external disk would be that I’ll use for backups. I include backup costs/methods whenever I purchase disk updates.
Any comments on that?
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