Re: LVM, Raid, and USB Harddisks

["Tim Grossner" <tim@grossner.net>]

LVM mirroring would be ideal if that is possible. I will look into that today. One thing that scares me though, I ran into some issues with this USB HD running off of a PCI USB controller...after a few minutes of heavy r/w, the USB controller seemed to reset, and all of a sudden the disk that was on /dev/sda was reseen as /dev/sdb, and again vice versa a few minutes later. This was all happening while xfering a large bunch of files. I haven't got the error message I saw handy, but it was some sort of I/O issue.

On 5/12/07, Danny Sauer <danny@dannysauer.com> wrote:

Tim wrote regarding 'LVM, Raid, and USB Harddisks' on Sat, May 12 at 01:26:
> I am in the process of overhauling my home server. I have about 300+Gig in
> internal HD space, in a VolumeGroup. I also have a 320 Gig external HD via
> USB2.0. What I am wondering is, can I create a software Raid-1 array
> consisting of the VolumeGroup and the external disk? Is there a concern over
> differences in read/write speed of the two different sides of such an array?

Yes, you can use an LVM volume as part of a software raid.  I'm not sure
if that's a great idea, given that you give up some of the cool LVM
features if you're using md on top of it (resizability is the only one
that comes to me off the top of my head).  Also note that your boot
order might need changed - most distros are usually going to start RAID
devices first, then start LVM after.  Most of us who use both are
running LVM on top of a RAID volume set, not vice-versa.  Using EVMS for
management might make that easier, since it *should* figure out the
order for itself.

I would think that if you wanted to merge disks together (say you have a
200 and two 100s), you'd probably want to use RAID-0 underneath instead
of the device mapper.  You could still do that.  Just move the data to
the external drive (which is one disk in a raid-1 setup), redo the
internal drive, create a raid-0 from the internal drives, add them to
the raid-1, activate the new device in the raid1 which will rebuild the
array, enjoy.  Right?

You might also consider looking into the mirror target for LVM.  I
thought you could do volume mirroring without having to use the md
system.  But then, maybe I'm confused...  Maybe the mirror target is
just for snapshot volumes?

--Danny

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-- 
________________
Tim Grossner
tim@grossner.net
There is no place like ~/.