On 7/12/2010 1:45 PM, Arcady Genkin wrote:
> Creating the ten 3-way RAID1 triplets - for N in 0 through 9:
> mdadm --create /dev/mdN -v --raid-devices=3 --level=raid10 \
> --layout=n3 --metadata=0 --bitmap=internal --bitmap-chunk=2048 \
> --chunk=1024 /dev/sdX /dev/sdY /dev/sdZ
>
> Then the big stripe:
> mdadm --create /dev/md10 -v --raid-devices=10 --level=stripe \
> --metadata=1.0 --chunk=1024 /dev/md{0,5,1,6,2,7,3,8,4,9}
I must admit, that I haven't seen a software RAID implementation where
you create multiple devices from the same set of disks, then stripe
across those devices. As such, when using LVM, I'm not exactly sure how
the kernel will handle that- mostly if it will see the appropriate
amount of disk, and what physical extents it will use to place the data.
So for me, this is uncharted territory.
But, your commands look sound. I might suggest changing the default PE
size from 4MB to 1MB. That might help. Worth testing anyway. The PE size
can be changed with 'vgcreate -s 1M'.
However, do you really want --bitmap with your mdadm command? I
understand the benefits, but using 'internal' does come with a
performance hit.
> From the man page to 'lvcreate' it seems that the -c option sets the
> chunk size for something snapshot-related, so it should have no
> bearing in our performance testing, which involved no snapshots. Am I
> misreading the man page?
Ah yes, you are correct. I should probably pull up the man page before
replying. :)
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