[Dirvish] LVM2 and dirvish

Nathan Hunsperger dirvish at hunsperger.com
Sat Feb 26 15:02:24 PST 2005

On Sat, Feb 26, 2005 at 12:30:23PM -0800, Keith Lofstrom wrote:
> Keith wrote:
> ...
> > per track.  So the table generated by "sfdisk -d" was not directly
> > usable as input to the new sfdisk.  I had to do an fdisk by hand.
> > 
> On Fri, Feb 25, 2005 at 04:00:39PM -0500, Jason Boxman wrote:
> > I've been using LVM2 of late and liking it a lot.
> Tell us more!

Figure I'll chime in here too.  I'm also using LVM2, but in a different
manner than what has been discussed so far; I'm using LVM for the
backup volumes, rather than for the backed-up volumes.  In my setup, I
have a dedicated backup server with a 600GB software raid5 filesystem,
in addition to the root fs.  This server currently serves backups over
NFS for 3 file systems.

I really like LVM, as it prevents locking yourself into a corner with
respect to partition sizes.  So far, the ability resize file systems
has been very useful; I have grown and shrunk the backup filesystems as
necessary to accomodate disk upgrades on the different backed-up servers.
There are several utilities available (at least for ext3) that allow
you to resize the file system and logical volume in the correct order
to prevent data loss...I have even successfully done this on a live
file system.

While you can still resize file systems w/o LVM, it requires that you
have contiguous space after the partition.  With LVM, this is no longer
the case.  When I need more backup space in the future, I plan to grow
my filesystems into any available free space, and then across another
physical raid5 volume.

I'm not sure which distros contain LVM2 support by default.  However,
the LVM2 patches from sistina apply very cleanly if you compile your
own kernels.

One note:  In several guides on using Dirvish, there is talk about
changing the size of blocks to maximize storage.  If you do so, and
are using linux software raid5, make certain that every filesystem on
the raid5 volume has the same block size.  If you don't, your raid5
performance will be pathetic, as linux will flush the block cache every
time an I/O request is made for a different block size.  This also has
the side effect of filling up /var/log quite quickly.

- Nathan

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