dm-raid1 improvements
dm-raid1 improvements
Posted Apr 20, 2008 8:10 UTC (Sun) by wolfgang.oertl (guest, #7418)In reply to: dm-raid1 improvements by sbergman27
Parent article: Stable kernel 2.6.25 released
I'm not familiar with Fedora, but you can check whether your setup uses the device mapper or the "md" drivers: type "mount" - if you see lines like /dev/mapper/some-thing then dm is used, and you don't have read balancing yet. OTOH if /dev/md0 and similar is mounted, this is not an issue. Another option is to monitor drive activity with some GUI tool to see whether reads are distributed to all drives of the raid, or have a look at /proc/partitions to check the read counters.
Posted Apr 20, 2008 10:46 UTC (Sun)
by nix (subscriber, #2304)
[Link] (3 responses)
/dev/raid/root 198344 47412 140692 26% /
md1 : active raid5 sda6[0] hdc5[3] sdb6[1]
76807296 blocks super 1.2 level 5, 64k chunk, algorithm 2 [3/3]
[UUU]
[...]
Checking whether you are using the device mapper is not the same thing as
checking whether you are using dm-raid.
Posted Apr 20, 2008 17:59 UTC (Sun)
by sbergman27 (guest, #10767)
[Link] (2 responses)
Posted Apr 20, 2008 18:21 UTC (Sun)
by nix (subscriber, #2304)
[Link] (1 responses)
Posted Apr 20, 2008 18:44 UTC (Sun)
by sbergman27 (guest, #10767)
[Link]
Really?
dm-raid1 improvements
nix@loki 10 /home/nix% df -Pk /
Filesystem 1024-blocks Used Available Capacity Mounted on
Oh, I can't be using md then: odd, I didn't know they had RAID-5 md-raid
yet.
Personalities : [raid1] [raid6] [raid5] [raid4]
Hint: dm allows for a stack of block devices, and you can layer md
both above it and (more usefully) below it. This particular system is
using the fairly common configuration of LVM-atop-MD, thus is a dm-atop-md
system.
dm-raid1 improvements
Well, I am using the mapper. And if I dd from the /dev/mapper/VolGroupxx/LogVolxx/ to
/dev/null and then do the same with /dev/sdax, which is the first member of the raid1 array, I
get about 61MB/sec in both cases. So I guess I'm not getting read balancing in F8. Or, come
to think of it, is the read balancing that fine-grained? I recall somebody telling me, a
while back, that it only balanced reads from different processes, and not from the same
process, or something like that.
dm-raid1 improvements
I can't imagine dm could tell which process was originating the request,
even if it wanted to. It's all one by that point.
dm-raid1 improvements
Seemed odd to me, too. Another odd thing is that this kernel release, which I had not really
thought was anything all that special, actually has not one, but at least two bombshell
features. How did I miss the loud outcry which surely occurred when read balance support in
raid1 was lost? And why have both its return, and the new TASK_KILLABLE functionality gotten
so little notice?