Thanks to:
"Dave Golden" <golden_at_falcon.invincible.com>
Paul Rockwell <rockwell_at_rch.dec.com>
that both indicated that, yes I can create multiple logical drives
on the same drive group and preserve the maximum storage space when
running RAID 5.
Dave provided a detailed procedure to transfer my partitions to the
new disks. And Paul also mentionned that running running RAID 5
on high write partitions, such as /var, carries a penalty.
Thanks again!
Yvon L.
============================================================================
From: "Dave Golden" <golden_at_falcon.invincible.com>
X-Mts: smtp
> My first problem is with the configuration of the RAID controller and the
> migration of all the partitions to the new disks. I would like to run
> everything with RAID 5 and have the most space available (20GB). The
> way I understand it I can only create one logical drive (RAID 5) per
> drive group and label the one BIG logical drive into multiple partitions.
> Or can I create 5 logical drives of 4Gb each and still retain 20GB of space?
You can create multiple logical drives on the same physical drive group.
>
> My second problem is to be able to migrate my root and /usr partitions to
> the new drives or partitions without to much problem. Any thoughts on
> doing this?
After you build support for the RAID controller into your kernel,
Boot to single user mode, run /sbin/bcheckrc to mount /usr and / writable,
use MAKEDEV to create /dev/re0 (the first logical drive on your RAID
controller),
use disklabel -t advfs -wr /dev/rre0c SWXCR to label your
new disk and write the bootblock out,
use mkfdmn to create a new_root_domain on partition a and a new_usr_domain
on partition g on /dev/re0
use mkfset to create a root fileset on new_root_domain and a usr fileset
on the new_usr_domain,
use vdump and vrestore to copy your existing root fileset to the new root
fileset and the same with usr,
mount the new root fileset and fix up the device references in /etc/fstab
and the links in /etc/fdmns/root_domain and /etc/fdmns/usr_domain
shutdown and boot from dra0
(Can't tell I've had to do this before, can you?)
good luck,
Dave
=============================================================================
From: Paul Rockwell <rockwell_at_rch.dec.com>
Subject: Re: Migrating to RAID 5
At 02:37 PM 2/29/96 -0500, you wrote:
>My first problem is with the configuration of the RAID controller and the
>migration of all the partitions to the new disks. I would like to run
>everything with RAID 5 and have the most space available (20GB). The
>way I understand it I can only create one logical drive (RAID 5) per
>drive group and label the one BIG logical drive into multiple partitions.
>Or can I create 5 logical drives of 4Gb each and still retain 20GB of space?
I believe that you can create multiple logical drives on the RAID controller
out of one drive group. I've done it with mirrored sets... And yes, you still
get 20GB of space.
However, you have to think of the performance impacts of what you're doing.
Multiple partitions or multiple drive groups may not give you good performance
depending upon the workload. There's a possibility of sending the disks
thrashing as you access different partitions/logical disks,although the
striping of RAID-5 may help out somewhat.
>My second problem is to be able to migrate my root and /usr partitions to
>the new drives or partitions without to much problem. Any thoughts on
>doing this?
Stuff that has moderate to heavy write loads I absolutely would not migrate
to a RAID-5 solution. Even with cache, RAID-5 writes carry a penalty.
Root may be OK, but /usr (that contains /var) I wouldn't put on a RAID-5 set.
That's better off on a 0+1 set, IMHO.
Also, remember that if you're moving your existing disks onto the KZPSC, then
you have to back them up first. The RAID array firmware writes a private area
onto the disk, changing the usable size of the disk. That means that your
existing partition table on the disk (if it survives this writing of RAID
control information - I'm not sure if it's at the beginning or end of the disk)
is invalid.
Also, if you're running RAID-5 on the KZPSC, I hope you bought the battery
backup for the cache option. RAID-5 performs much better with it, as it's
then possible to run the caches in write-back mode instead of write-through.
--------
+---------------------------+ Paul E. Rockwell
| | | | | | | | Northeast Region SBU Technical Support
| d | i | g | i | t | a | l | Digital Equipment Corporation
| | | | | | | | 500 Enterprise Drive
+---------------------------+ Rocky Hill, CT 06067 USA
http://www.digital.com Internet: rockwell_at_rch.dec.com
Telephone: (860) 258-5022
Received on Fri Mar 01 1996 - 20:05:09 NZDT