Re: For Lenny: LVM, LVM+MD or just MD for mirroring?
Jens wrote:
> Generally I would like to hear any experiences with LVM2 you can
> offer.
> The last time I tried LVM I hosed everything, but that was eight years
> ago, at least partly due to a user error, and with LVM1 on Debian
> Woody
> with a self-compiled kernel on 2.4.2x.
I would stick to MD for the RAID and LVM for the snapshot stuff.
It's been a while since I ran MD on Debian so I don't know how/if it
handles installing the boot loader to the other disk. Red Hat at least
did not by default and I put a workaround in my kickstart config to
take care of that for me.
I have used LVM/LVM2 quite a bit, though have never used snapshots.
The most use I got out of LVM was using it with a multipathed SAN,
over iSCSI and Fiber Channel. LVM allowed the system to find the
volumes no matter what path they were presented down(and with
software iSCSI the scsi devices changed every time iscsi was
restarted). So it was a real help. I limited my snapshots to the
SAN array itself, so I could snapshot the volume and export it
to another system to do no impact backups.
Also with LVM I was able to restrict volume sizes pretty easily
to allow for growth as the storage array presented the volumes
in a thinly provisioned form (some work loads don't agree with
thin provisioning so I could export a 2TB volume to the hosts,
restrict the file system to a couple hundred gig, and when I
needed more I just expanded the LVM, only space that was written
to was actually consumed on the storage end).
I believe with LVM and snapshots you have to set aside a
fixed amount of space to store the deltas for them when
configuring the volume group, though this may of changed.
If using MD with LVM sounds too complicated you should consider
a hardware RAID controller, that way you don't need to worry
about boot loaders and 2nd disks, or rebuilding the array etc..
For me, multiple simple layers are easier to work with than
fewer more complicated layers.
nate
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