From: Felecia Diggs (FeleciaDiggs@schev.edu)
Date: Wed Jul 16 2003 - 10:20:55 EDT
Thank you Ingo, NetComrade, Terry, Eric, Eugene, Danny, and Ryan for
your responses. I appreciate your sharing your experience with this
issue.
My original question was as follows:
Has anyone out there had success in mirroring 2 disks of different
disk
geometries? Also what problems if any did you experience?
Particularly, if you experienced a failure on the primary, were you
able
to keep your system up and running via the secondary or vice versa?
Thanks in advance for your input.
Below in quotes are the responses I received.
" I'm doing this with a Solaris 8 for Intel. First disk is a scsi,
second one an ide.
The system was already running on the scsi disk. Because of the
different geometry
between ide and scsi, i created the slices on the ide disk a bit
bigger. Mirroring works fine.
With the kdm boot disk, i can also boot the second (ide) disk. Even the
upgrade to solaris 9
worked fine."
"if you're mirroring an 8G volume/subdisk system on a 9G disk to an
18G
disk, it's no problem (in veritas VM)."
"I've been successfully using DiskSuite and mirroring different disks.
Just make sure that your slices that you're mirroring are at least the
same size if not slightly larger."
"It works...it's not ideal, but it works."
"Yes, It can be done.
Normally the problems are secondary with workarounds:
1) Creating a partition for mirroring, can result in one or two block
sizes
diff. Allow for this.
2) Allow for speed variances e.g: 7200 RPM and 10000 RPM - set
preferred
read policy on the fastest if a disk I/O bottleneck is observed on the
slower disk. A failure on the faster disk will allow reads from the
slower
disk.
3) If sizes are different, allow for even spread of I/O. (If one root
disk
is 9GB, one 18GB, what do I put on the balance - watch out for
contention
here as well)
My advice would be to avoid if possible. A symmtrically laid out
system
normally makes for easier maintenance.
If possible re-layout as soon as possible later if it is not an option
currently (and the reason for tyour question).
Upgrade (IF a Sun disk) one existing disk to larger capacity to allow
for
symmetrical layout. With Sun's upgrade policy you have some time to
migrate
before having to return the old disk. While this does not save a lot
of
money, it does help take the bite out of the price. Also consider Sun
refurb
disk if cost is an issue. (Rather buy two refurb disks than one new one
and
avoid geometry issues)
The bottom line: Yes it can be done, but the management side normally
bites"
"Wouldn't recommend it.
It will/could work, but I would not configure a critical system mirror
with 2 disks of different geometries. There's no guarantee on what
will
happen when one of them dies."
"The one thing that you must be aware of is that the primary disk CAN
NOT be
bigger than the mirror disk. With that being said, the mirror disk
can
obviously be bigger than the primary disk of the system. I have ran a
system like this before but I did not have to face an issue with losing
a
disk."
Felecia F. Diggs
Unix Administrator
State Council of Higher Education for VA
(804) 225-2643
Email: feleciadiggs@schev.edu
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