mlelstv%serpens.de@localhost (Michael van Elst) writes: > jeanyves.migeon%free.fr@localhost (Jean-Yves Migeon) writes: > >>[...] the first few minutes of the >>parity rebuild go fine, both disks working at about 20-25MiB/s (which is >>their nominal speed when used in !raid setup). >>But after that, the rebuild I/Os slow to a crawl to a mere 2-3MiB/s and >>it remains stationary. > > The raid1 rebuild procedure compares both disks and when it finds > differences it copies the data. Switching between continous reading > and writing can slow down the operation significantly, in particular > when RAID stripes and disk tracks are not aligned. It can be even > slower when for some reason only writing to a disk is slow. Interesting - I had no idea there was a read/write check cycle - I thought it just wrote (for RAID1 anyway, which is all I use). My own experience with rebuild of RAID1 is that they tend to go smoothly at disk speed the whole time. FWIW, my preferred tool for watching this is "systat vmstat" which has not only IOPS and MB/s but % busy.
Attachment:
pgpJmmtCZW8Cq.pgp
Description: PGP signature