[ENBD] Re: Problem with software RAID1

[P.T. Breuer]

In article <1079694313.1544.8.camel at Rafke> you wrote:
> I've configured a raid1 with a local raid disk and a remote disk with
> enbd. The size of partition is about 55 Gb.  (the hardware of the two
> nodes is exactly the same)
> 
> raiddev /dev/md0
>         raid-level 1
>         nr-raid-disks 2
>         nr-spare-disks 0
>         chunk-size 32
>         persistent-superblock 1
>         device /dev/sda9
>         raid-disk 0
>         device /dev/nd/a/0
>         raid-disk 1
> 
> The time to synchronise (over a 1000BaseT) is not symetric :
> 
> from /dev/sda9 to /dev/nd/a/0 it's take 50 minutes and from /dev/nd/a/0
> to /dev/sda9 it's take 500 minutes. Which could be the reason of this
> differences.

Almost anything. How about measuring the read and write times to and
from various devices without raid in the middle? That would give us
more data.

(I would guess that blksize mismatches account for at least some of
that, but many other things could be involved - enbd goes at overspeed
during writes, for example, because it skips blocks that are already
equal both sides, and that could account for some more of the
difference).


Peter