[rhelv6-list] mdadm rebuild
Jason Keltz
jas at cse.yorku.ca
Mon Oct 20 16:07:07 UTC 2014
Hi.
I'm creating a 22 x 2 TB SATA disk MD RAID10 on a new RHEL6 system. I've
experimented with setting "speed_limit_min" and "speed_limit_max" kernel
variables so that I get the best balance of performance during a RAID
rebuild of one of the RAID1 pairs. If, for example, I set
speed_limit_min AND speed_limit_max to 80000 then fail a disk when there
is no other disk activity, then I do get a rebuild rate of around 80
MB/s. However, if I then start up a write intensive operation on the MD
array (eg. a dd, or a mkfs on an LVM logical volume that is created on
that MD), then, my write operation seems to get "full power", and my
rebuild drops to around 25 MB/s. This means that the rebuild of my
RAID10 disk is going to take a huge amount of time (>12 hours!!!). When
I set speed_limit_min and speed_limit_max to the same value, am I not
guaranteeing the rebuild speed? Is this a bug that I should be
reporting, or a "feature"?
Jason.
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