[linux-lvm] Software RAID on LVM

[linux-lvm] Software RAID on LVM

[fox]

Hi;

I've been on the list for a few days now and I'm starting to get a sense
of what LVM can an cannot do (I come from AIX's LVM and I'm happy to see
Linux is starting to have something similar)

One thing I've not gotten a full sense of is can you have a RAID 1 array
sit ontop of a LVM filesystem?  I understand that LVM does not have any
internal RAID capabilities (that's the sense I've been getting...though I
might be on glue...never count out that possibility with me ;) but might
be possible to have the internal Software RAID in Linux to sit ontop of a
filesystem using the LVM.

Also, what type of filesystem is recommended for use with LVM (and
possibly RAID 1?  I'm quite hopeful for that...)  I'm thinking ReiserFS is
the FS of choice here, but would anyone mind clairifying for me why it
would be better, or which you think would be better?

Thanks for your time to read this newbie LVM post.  =)

Cheers,

Tren.

Re: [linux-lvm] Software RAID on LVM

[Joe Thornber]

On Thu, May 03, 2001 at 06:06:41AM -0600, fox@theendoftime.net wrote:
> Hi;
> 
> I've been on the list for a few days now and I'm starting to get a sense
> of what LVM can an cannot do (I come from AIX's LVM and I'm happy to see
> Linux is starting to have something similar)
> 
> One thing I've not gotten a full sense of is can you have a RAID 1 array
> sit ontop of a LVM filesystem?  I understand that LVM does not have any
> internal RAID capabilities (that's the sense I've been getting...though I
> might be on glue...never count out that possibility with me ;) but might
> be possible to have the internal Software RAID in Linux to sit ontop of a
> filesystem using the LVM.

It depends on the kernel version that you are running.  On 2.4.x
kernels you should be able to run LVM and software raid on top of each
other (this is not something I've tried but I believe other people are
doing so).

With 2.2 kernels I have provided a patch (see LVM/PATCHES/README)
which should allow you to stack LVM on top of software RAID, but not
the other way round.

> Also, what type of filesystem is recommended for use with LVM (and
> possibly RAID 1?  I'm quite hopeful for that...)  I'm thinking ReiserFS is
> the FS of choice here, but would anyone mind clairifying for me why it
> would be better, or which you think would be better?

I don't think any particular fs stands out for use with LVM; choose
the one with the characteristics you want.  I'm sure you can dig up
reiserfs vs. ext2 comparisons on the web.

- Joe

Re: [linux-lvm] Software RAID on LVM

[Evan Day]

fox@theendoftime.net wrote:
> One thing I've not gotten a full sense of is can you have a RAID 1 array
> sit ontop of a LVM filesystem?  I understand that LVM does not have any
> internal RAID capabilities (that's the sense I've been getting...though I
> might be on glue...never count out that possibility with me ;) but might
> be possible to have the internal Software RAID in Linux to sit ontop of a
> filesystem using the LVM.

I run LVM on top of a RAID-1 array (i.e. pvcreate /dev/md0).  I tried it the
other way around (RAID-1 on LVM, i.e. /dev/md1 and /dev/md2 in the raidtab), 
but ran into problems with device numbering changing between configuration
and rebooting, but I never did try to resolve it.  It would be great to have
LVM do logical volume level mirroring like HP-UX LVM, but not necessary
since the kernel does RAID separately (unlike the HP-UX kernel).

> Also, what type of filesystem is recommended for use with LVM (and
> possibly RAID 1?  I'm quite hopeful for that...)  I'm thinking ReiserFS is
> the FS of choice here, but would anyone mind clairifying for me why it
> would be better, or which you think would be better?

I like reiserfs - as mentioned before it is a little easier to resize than
ext2, journaling is nice if you want quick repairs, and it has some 
interesting features coming down the pipe along with anticipated increases
in performance as the code base matures.  I'm using reiserfs now and have
had zero problems (so far) and have already taken advantage of the ability
to resize mounted filesystems several times.

-Evan