Re: Raidframe low I/O for parity rebuild, but when accessed through rraid* devices

[mlelstv%serpens.de@localhost (Michael van Elst)]

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.

-- 
-- 
                                Michael van Elst
Internet: mlelstv%serpens.de@localhost
                                "A potential Snark may lurk in every tree."