Re: stride / stripe alignment on LVM ?

On Thursday November 1, janek_listy@wp.pl wrote:

Hello,

I have raid5 /dev/md1, --chunk=128 --metadata=1.1. On it I have
created LVM volume called 'raid5', and finally a logical volume
'backup'.

Then I formatted it with command:

   mkfs.ext3 -b 4096 -E stride=32 -E resize=550292480 /dev/raid5/backup

And because LVM is putting its own metadata on /dev/md1, the ext3
partition is shifted by some (unknown for me) amount of bytes from
the beginning of /dev/md1.

I was wondering, how big is the shift, and would it hurt the
performance/safety if the `ext3 stride=32` didn't align perfectly
with the physical stripes on HDD?

It is probably better to ask this question on an ext3 list as people
there might know exactly what 'stride' does.

I *think* it causes the inode tables to be offset in different
block-groups so that they are not all on the same drive.  If that is
the case, then an offset causes by LVM isn't going to make any
difference at all.

NeilBrown

PS: the resize option is to make sure that I can grow this fs
in the future.

PSS: I looked in the archive but didn't find this question asked
before. I'm sorry if it really was asked.

Thanks for trying!