Expanding RAID5 guidance

Jeff Boyce jboyce at meridianenv.com
Mon Feb 2 13:17:14 CST 2009


Thanks for the input.  I think this gets me a little closer.  I am posting 
more input at the bottom.

----- Original Message ----- 
From: "Ryan Bair" <ryandbair at gmail.com>
To: "Jeff Boyce" <jboyce at meridianenv.com>
Cc: <linux-poweredge at dell.com>
Sent: Sunday, February 01, 2009 12:06 PM
Subject: Re: Expanding RAID5 guidance


> 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
>

Ryan -

I agree with your personal recommendation (backup and restore onto a fresh 
setup), however I can't meet the assumptions you have made.  I only have the 
one server in the company, no spares, no VM, nada; and I would have loved to 
have LVM on this system, but I did not set it up 5 years ago.  This system 
also contains my tape backup software (not something I want to reinstall 
from scratch).  So I have to work with what I have in front of me.  Also 
since I mentioned that it is a small business, admin'ing the server is only 
a part time thing for me, my full time responsibility is as a consulting 
forester.  So one of my goals on this task is to minimize the potential for 
me making a mistake that could cost a lot of my time to restore a system 
from scratch.

Thanks for the advice on the partitions.  It looks like if I really knew 
what I was doing I could expand the sda10 (ecosystem) partition to take up 
the new space, but none of the other partitions.  From this advice I will 
probably consider just adding a new partition and then reorganizing my file 
directory system to use it in an appropriate way.  I don't think that would 
be too much of an inconvenience to our users (all 9 of them) and might be my 
safest approach for minimizing mistakes.

So I am down to needing a few pieces of information:
   1.  How do I create a new partition sda11 on my expanded raid5?  Is this 
with fdisk?  With disks mounted or unmounted?
   2.  How do I expand the file system?  Is this with resize2fs?  With disks 
mounted or unmounted?
   3.  Then I assume that I need to create a new entry in fstab?
   4.  Then do I need to reboot in order to verify that I have the correct 
entry in fstab?

Thanks,
Jeff



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