Linux - CentOS5 and software raids.....

We all like RAID, and with Linux it's a pretty cheap way to get enough space to store ones DVD/Music collection, I run a fairly large RAID5 which is working without a hiccup, but much to my surprise I was checking my /proc/mdstat and saw:

md5 : active raid5 sdh1[4] sdg1[3] sdf1[2] sde1[1] sdd1[0]
7814033408 blocks level 5, 64k chunk, algorithm 2 [5/5] [UUUUU]
[================>....] resync = 81.5% (1593083392/1953508352) finish=2362.7min speed=2540K/sec

Then I checked dmesg, and /var/log/messages, no errors, no nothing so how could that happen, after a bit of searching I found a long discussion - it seams that after CentOS 5.4 they decided to add /etc/cron.weekly/99-raid-check which is controlled by /etc/sysconfig/raid-check - which by all means is fair, but but with a rebuild speed of 2540K/sec and more than a 7TB raid this might take slightly more than a week.

One can move the check to run only ones a month by moving the script from cron.weekly to cron.monthly, but it will still take time.

In general there is nothing wrong with running a resync on a raid, but it can take some time, and it should not be run every week, and if it is they should have have forced the speed up to something like 20000K/sec or at least have made it configurable. Especially for us who have a controller which can handle +100000K/sec


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