Re: [opensuse] mdadm --grow
- From: "Greg Freemyer" <greg.freemyer@xxxxxxxxx>
- Date: Thu, 30 Oct 2008 08:48:41 -0400
On Thu, Oct 30, 2008 at 8:02 AM, Per Jessen <per@xxxxxxxxxxxx> wrote:
Greg Freemyer wrote:
All,
I'm conceptually putting together a NFS server in my head. (I will
build it once I know what it is!!)
What I want is something flexible.
ie. Have it start with 3 or 4 drives, then add a drive when I need the
capacity. Remove a drive when I don't. replace the drives with bigger
drives as the become available. All without losing my data. (Or
having to back it up / restore it.)
My first thought - LVM.
I'm very familiar with LVM. It does not really do the same things as
RAID. Not even if you only worry about the performance side of
things. ie. a 4 disk raid system is faster than a single disk for
most raid setups. With LVM based on 4-drives, it is typically just
the same speed as a single disk.
I'd like to start with a 4 disk Raid 10 providing 2 TB of space, but
then have the ability to add disks, change raid techniques etc. (ie.
convert to raid 6 without data loss!!).
mdadm --grow implies it can do this, but there is not much there and
my google searches did not turn up much either.
I don't think mdadm --grow can do what you want. It's very useful when
you for instance want to build a RAID1 in degraded mode (with only one
drive), and you later want to add a drive to bring it back to full
RAID1. You can probably also add a drive to working RAID1 or maybe
even RAID5, but I don't know.
The man page says it can change the "size or shape" of a raid array.
But then provides no detail. :( I'm assuming shape means the raid
level? Not a phrase I know in reference to raid.
And can it be used to "shrink" a volume. (I believe XFS supports
shrinking a filesystem, so I would first shrink the filesystem, then
hopefully use mdadm to shrink the raid array.)
Most advanced filesystems (jfs,xfs,ext3 et al) support resizing -
otherwise the LVM resizing features wouldnt be overly useful :-)
I know most can grow. iirc, only xfs can shrink?
If mdadm can't do any of this, is there a hardware controller card
that can?
Take a good look at LVM.
Actually I came across the QNAP TS509 yesterday. A very cool NAS
that seems to do everthing I want. It is Linux based and provides ssh
access. I assume you can use that access to admin things if need be.
Its about $1000 for an empty shell that holds 5-drives.
Greg
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/Per Jessen, Zürich
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