Re: how to use mkfs.ext3 "stride=" on LVM on RAID correctly?

[Michal Soltys <soltys@ziu.info>]

Tomasz Chmielewski wrote:

> Although the fine mkfs.ext3 manual gives some basic information on how 
> to do it if you place the whole filesystem on a RAID array, it is not 
> clear to me how it should be done correctly if I want to create a ext3 
> filesystem on LVM on RAID-5.
> 
> Any helpful hints?

You should be careful with all the alignemnts. Extents should be properly 
aligned with - at the very least - stripes, and preferably with whole stripe 
width (not always possible though). To check where lvm extents, you can use 
i.e.:

dmsetup table
pvs -o+pe_start --units s
losetup and hexedit experiments (silly, but I used to do it like that in the 
past, before I realised about other options :o )

If you don't need default 4M granularity, it's nice to increase it (vgcreate 
-s option ; I use 256M and 512M sized extents). You can alter the beginning 
of the extents with --metadatasize option of pvcreate (overally it always 
rounds up to the next 64K multiple). Be sure to verify with one of the 
commands above.

Moreover - if you use partitionable raid and create lvm in one of the 
partitions, make sure partition is properly aligned as well.