On Sun, 2008-09-21 at 21:01 +0200, Kay Diederichs wrote: > Fact is that with CentOS-5 kernels (but not with CentOS-4, as this > functionality became available in kernel 2.6.17) you could (or rather > _should_ regularly) > echo check > /sys/block/mdX/md/sync_action > to check agreement between the two (or more) copies. When this finishes, > /sys/block/mdX/md/mismatch_cnt shows you the number of mismatches. You > can fix these with > echo repair > /sys/block/mdX/md/sync_action Interesting. I'll give this a go on my own desktop system which is running RAID 1. You said above, "When this finishes...", but how do you know the check is completed? I saw this in /var/log/messages: Oct 1 11:02:47 ranbir kernel: md: data-check of RAID array md0 Oct 1 11:02:47 ranbir kernel: md: minimum _guaranteed_ speed: 1000 KB/sec/disk. Oct 1 11:02:47 ranbir kernel: md: using maximum available idle IO bandwidth (but not more than 200000 KB/sec) for data-check. Oct 1 11:02:47 ranbir kernel: md: using 128k window, over a total of 104320 blocks. Oct 1 11:02:48 ranbir kernel: md: md0: data-check done. Oct 1 11:02:48 ranbir kernel: RAID1 conf printout: Oct 1 11:02:48 ranbir kernel: --- wd:2 rd:2 Oct 1 11:02:48 ranbir kernel: disk 0, wo:0, o:1, dev:sda1 Oct 1 11:02:48 ranbir kernel: disk 1, wo:0, o:1, dev:sdb1 There was nothing else after the last line. I don't know exactly what the "disk" lines mean. Regards, Ranbir