Expanding RAID5 guidance

Ryan Bair ryandbair at gmail.com
Sun Feb 1 14:06:03 CST 2009


Hi Jeff,

Since no one has bitten, I'll throw in my $0.02.

On Fri, Jan 30, 2009 at 5:33 PM, Jeff Boyce <jboyce at meridianenv.com> wrote:
> Greetings -
>
> I am a novice Linux user that manages a file server for a small business and
> am looking for a little general guidance on understanding the right steps
> for expanding the storage capacity on a Dell Server.  Sorry for the long
> post, but I know how irritating it is when people don't describe their
> objective or provide all the details for someone else to understand the
> problem.
>
> Existing Server Setup:
>   Dell PE 2600
>   PERC 4/Di
>   3 - 36GB hard drives in Raid5
>   1 - 36GB dedicated hot spare
>   No LVM used
>   RHEL 3 update 9
>   OMSA 5.1
>   Used as small office Samba file server
>
> Proposed Objective:
>   Add 2 - 36GB drives in remaining spare slots
>   Expand Raid5 to include the added space
>   Make use of the added space by users of the file server
>
> I know the first rule of thumb with managing raids and file systems is to
> have good backups (multiple backups are better) and I am writing up a
> detailed list of additional files to backup besides my home and data
> directories, so I think I have this covered.  My second task has been to
> make sure that I have a rescue disk or reinstallation disks available in
> case its needed.  If OS installation becomes necessary for some reason I am
> considering upgrading to 5.2 (but that is beside the point).
>
> I have read through the OMSA user guide and feel comfortable going through
> the task to physically install the new drives, and the steps for
> reconfiguring the existing virtual disk.  This point is were my information
> and comfort level begins to fall apart.  The first questions that I would
> like answered is:
>
> 1.  How long does the reconfiguration process take (I will do this on a
> weekend when no one is using the system)?

I'd certainly leave a weekend just in case things go terribly wrong.
The drives are pretty small so I wouldn't expect it to take over an
hour to resize the array but I've never resized on a PERC4.

> 2.  How do I know when the reconfiguration process is done (something the
> user guide doesn't describe)?  As you can see I want to know what to expect
> (good or bad) prior to completing the reconfiguration.

The console should list the process and its percent completion.

> Then from my reading of numerous descriptions of expanding raids through
> google searches (including a decent summary of the steps written by Matt
> Domsch (Expanding Storage on Linux-based Servers, Feb. 2003) it appears that
> I will need to expand the file system to use the new space; but do I also
> need to add/create a new partition for this space, or can I expand an
> existing partition into this space.  What I would like to do is just expand
> one or two existing partitions and distribute this space among them, if that
> is possible (see fstab listed below).  So my next questions would be:
>
> 3.  What are the general steps that I need to do after my raid
> reconfiguration is complete to achieve my general objective?
> 4.  Would it be possible to add the new space to one or two existing
> partitions?  I am thinking sda2 and sda10 (/ecosystem is our samba share
> data directory that would be given 90% of the new space).
> 5.  Will I need to add/create a new partition (and samba mount point) to
> make use of the new space?  If so I could reorganize our data files to make
> use of two samba mount points.
> 6.  Any other pitfalls I should be aware of, such as what steps need to be
> done on unmounted drives?

This will be very tricky, especially since no volume manager is being
used. You can resize a partition, but it must be contiguous. So to
expand anything other than the last partition, you'll need to play
musical file systems which will be tedious and error prone. You could
also just make a new partition and make a filesystem on it, but that
would probably be the least friendly to the users of the system.

Personally, I would backup the current system, test the backup (on a
spare system or on a VM) and manually restore to a fresh setup
preferably with LVM for everything but /boot. This will involve
manually creating the physical and logical volumes, transferring the
data back, and setting up the bootloader and fstab. However, I am
completely crazy. Don't try this unless you're 100% positive your
backups actually work and you've planned the whole process and did a
dry run.

> Thanks for any and all comments and suggestions; good howto links are always
> welcome.
>
> FSTAB
> -------------------------
> LABEL=/                 /                       ext3    defaults        1 1
> LABEL=/boot             /boot                   ext2    defaults        1 2
> none                    /dev/pts                devpts  gid=5,mode=620  0 0
> none                    /proc                   proc    defaults        0 0
> none                    /dev/shm                tmpfs   defaults        0 0
> LABEL=/tmp              /tmp                    ext3    defaults        1 2
> LABEL=/usr              /usr                    ext3    defaults        1 2
> LABEL=/var              /var                    ext3    defaults        1 2
> /dev/sda9               swap                    swap    defaults        0 0
> /dev/sda2  /home  ext3  defaults 1 2
> /dev/cdrom              /mnt/cdrom              udf,iso9660
> noauto,owner,kudzu,ro 0 0
> /dev/fd0                /mnt/floppy             auto    noauto,owner,kudzu 0
> 0
> /dev/st0  /mnt/tape  ext3 noauto,owner,kudzu 0 0
> /dev/sda10 /ecosystem ext3 defaults 1 2
>
> RECENT LOGWATCH OUTPUT
> ------------------ Disk Space --------------------
> Filesystem            Size  Used Avail Use% Mounted on
> /dev/sda7             2.0G  1.5G  385M  80% /
> /dev/sda3             190M   54M  128M  30% /boot
> none                  501M     0  501M   0% /dev/shm
> /dev/sda8            1012M   33M  928M   4% /tmp
> /dev/sda5             9.7G  2.8G  6.4G  31% /usr
> /dev/sda6             9.7G  2.9G  6.3G  32% /var
> /dev/sda2             2.5G  2.0G  443M  82% /home
> /dev/sda10             40G   35G  3.7G  91% /ecosystem
>
>
> Jeff Boyce
> www.meridianenv.com
>
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>

Hope this helps,
--Ryan



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