SUMMARY: Veritas vs. Sybase mirroring

From: Michael Pavlov (
Date: Fri Mar 15 1996 - 15:01:43 CST

Original post:
1. Has anybody looked into the pluses and minuses of using
Veritas mirroring as opposed to SYBASE mirroring? I am interested
in knowing about reliability and administration issues.
I am especially interested in PERFORMANCE comparisons.
2. Is anyone running SYBASE 10.02 on Solaris 2.5 ?
Any horror stories ?
Any improovment over 2.4 ?

I got a few answers.
1) Majority prefers Veritas.
The reason - higher throughput and flexibility.
Some people mentioned hardware /software mirroring - technicaly speaking Veritas is a s/w
solution as I see it.
Good point came from Todd Boss - "...Each time you write to that volume [mirrored], the kernel
issues two write requests.." as opposed to SYBASE' "concept of primary disk--mirror disk"
2) No problems with 2.5 as per Greg Roberts
I am including all answers.

Salvatore Saieva <>
I'm considering the same issues now but with Veritas and Informix. My
thoughts are that if I'm likely to mirror other non-database disks using
Veritas (which I am likely to do) then it seems to make sense (at least
for consistency sake) to do all mirroring using Veritas. Veritas seems to
have a more flexible (customizable) failure detection and notification
scheme (via scripts/E-mail) than Informix does, this is a plus. I would be
interested in seeing a summary particularly regarding performance issues.

"Marks, Evan R" <>
We are running still on 2.3 (blech) and were told the following about
veritas vs sybase mirroring:
1. Veritas mirroring is faster
2. Using Sybase mirroring is the only way sybase can guarantee you will not
corrupt your database and does not officially support any other mirroring.
due to #2, we went with it, since data corruption is more of an issue than
speed (Greg Roberts)
I believe that sybase is tuned/developed to work best against raw disk partitions.
Using veritas, you are going through another level of disk i/o software. Does this
degrade performance??? I have no solid figure, but I personnally feel more comfortable
using a config that sybase has developed against rahter than find the problems myself.
I use ODS to mirror the /opt/sybase directory, but sybase mirroring to do the sybase
device mirroring. You could argue its better to keep with one solution if possible ...
personal choice I think ...
I am running 10.02 under Sol2.5 ... skipped right over Sol2.4. We've been up and running
on an 8 gig DB for 2 months now and experienced no problems.

George L. Roman
Mirroring through hardware is more reliable and runs faster. Additional
benefits can include hot-swap and disk sharing for increased
fault-tolerance. A drawback: configuring the raid array is non-trivial,
especially with unconventional partitioning schemes.

Todd Boss (Todd.E.Boss@Bell-Atl.Com)
ALWAYS use hardware mirroring over Sybase's internal mirroring. The
performance of Sybase's mirroring shrinks in comparison to doing a hardware
level mirroring, whether it be Veritas or whoever. My Ultimate source
is a top level Sybase technician, who i cornered and asked.

The primary reason is this; when you create a mirror using Veritas (and I
assume its Volume Manager here), you are modifying the kernel to perform
dual writes. Volume Manager mirroring does not use the concept of
primary disk--mirror disk; it creates a volume containing two disks, either
one of which can be considered the image or the source. Each time you
write to that volume, the kernel issues two write requests; if you spread
out the two images in a volume well enough you can obtain even better
write performance by utilizing more of the SCSI paths in/out of your disk

If you have a copy of Sybase's user manuals, esp. the Sybase 10 System
Administration guide (page 3-14) you'll see the difference. Sybase mirroring
makes you specify a primary and an image device; then each time the server
writes data to the primary, it issues a second, later transaction to write
to the mirror. Much less efficient that a dual kernel write. the Sybase
manual even tells you that mirroring reduces performance.

As far as reliability goes, i'd rather depend on a os-level mirror than
Sybase; as a sysadmin you have more control over devices through volume
manager than with Sybase; who knows what's going on with Sybase sometimes.
It takes on a life of its own.

Administration? Volume manager abstracts the concept of /dev/dsk/c?t?d?s?
to a higher level of just disks and volumes and disk groups. It takes some
getting used to; you'll have to learn a new way to administer disks, depending
on Volume Manager's gui/object command set. However, Volume Manager is
a fine configuration tool, much better than other Disk config tools i've used
(DG's dassmgr and gridman, IBM's piece of junk, HP, etc).

Tin-Lok Lam (
Yes. At least 30% faster, Danny says up to 50% more faster as he recalled
during the time we were testing the mirroring. The Cons is that if your system
crashes and put Veritas in an unstable state, getting the system
back on-line will heavily rely on Sun or Veritas support. However, this is
always the case no matter you are using Sybase mirroring or not since Sun Array
requires Veritas software. For example: if your system has a bad memory and
crashes the system, it will put Veritas in an unstable state.
I haven't had any problem mirroring Sybase using Veritas and we have been
using it for a while.

Thanks to:
bfr7kq6@is000913.BELL-ATL.COM (Boss) (Greg Roberts)
"Marks, Evan R" <> (George L Roman)
Salvatore Saieva <> (Tin-Lok Lam)


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