SUMMARY: SDS vs. Veritas

From: Leonid Massarskiy (
Date: Wed Sep 06 2000 - 14:59:15 CDT

Re-posting earlier message with SUMMARY in the subject line, so it gets


Thanks to:
Mark Neill
Michael Sullivan
Jed Dobson
Arthur Darren Dunham
for providing a very useful comparison between SDS and VxVM.
Here it goes:

Mark Neill:
Veritas is much more flexible - you can resize, add and drop mirrors, etc
etc etc, all on the fly with the system up (within constraints). Add
hot-swapable disks to this mix, and you really don't need to take the box
down for filesystem maintenance. All of this works better with VxFS as
well... SDS isn't very flexible. It requires at least 2/3rds of your
MetaDB's to be available to boot partitions, and doesn't like it or play
nicely when things start going wrong. However, it's MUCH easier to create
bootable mirrors with SDS than with Veritas.

We used to run both at my last job...SDS for the root disks, and VxVM for
the rest of the disks. We don't now, but are looking into moving that way
for DR purposes.

Michael Sullivan:

I like SDS for its simplicity from the command line and it has several
fewer levels of indirection. i.e. disk, sub-disk, plex, volume (with

Veritas is more felxible in the number of options and add on products.
This also adds to the complications of using it.

If you're doing anything serious with either, you will probably have
scripts to create objects. The GUI's are pretty, but impractical for
dealing with bulk drives. The Veritas command line is quite complicated
and getting things in the right order is a reach. Be prepared to repeat
the process several times to get it right.

Another thing is the concept Veritas has about disk groups. It's not
quite clear how one moves disks from one machine to another easily in
the even of failure.

In the end, SDS is clean an simple. Veritas is big, complicated, but
has lots of features.

Jed Dobson:
SDS free
VxVM $$$ (if not Sun Supported Storage (A5X00, T3)

SDS uses simple slices
VxVM uses plexes, volumes

SDS is easy to maintain
VxVM has a steep learning curve

SDS can't handle many things as "gracefully" as VxVM can.

VxVM has hooks for VxFS and a nice GUI (VMSA), its a standard across
platforms (HP/UX, Solaris and even NT, yes)

Here is a document describing them better. Its post script but a good
article. (LM: Attached to this messages too).

Arthur Darren Dunham:
Comes from sun.
Is free with any server license.
Uses existing slices on disks (limited to 8 on SPARC hardware).
Can create concat/stripe/raid5/mirror devices with or without logs.
User must specifically manage the VM database (replicas)
Naming convention limited to 0-127 for a disk group.
Root mirroring of 2 disks can cause boot problems after disk failure.
Will break if devices or controllers are renumbered.
Does not support multiple paths to devices.
Cannot enlarge slices on the fly, must use 'format' to do so.

Comes from Veritas
Licensed with Photon style arrays, or otherwise must be purchased.
Does not use existing slices (not limited to any specific number)
Can create concat/stripe/raid5/mirror devices. with or without logs.
User does not specifically manage the VM database, it is kept in a hidden
"private" region on each disk. Root mirroring can cause confusion during
any repair work due to changes bug will not hang on boot.
Will not break with any numbering or controller change.
Supports multiple paths to devices.
Can change slices in any manner.
Trivial to import configuration onto another machine.

Overall, SDS is a free product from sun, that uses existing slices on
disk for combination into larger volumes. You cannot create or destroy
mirrors on the fly, you must create a special "mirror" object and use
it. It works, but is limiting. If your controller changes number, the
database will become confused. You should generally allocate space for
the database and manage the replicas.

It's quite useful in the simple case of mirroring 2 root drives. The
one drawback is that with only 2 mirrored drives, SDS will not reboot
with a failed drive. You need to change the configuration after the
drive fails before it will boot again. This is not too big a problem,
but could be a concern for some shops.

VxVM is a much larger, more full featured product that is also
expensive. The flexibility of Veritas volumes is much larger than SDS,
and the database management virtually disappears (although you can
control it if you really want to).

This scheme does cause some to shy away from placing root disks under VM
control due to misunderstandings of what can and cannot occur in a
recovery situation when Veritas is unavailable.

Personally, in any situation more complex than a 2 drive root mirror,
I'd recommend the use of Veritas if the purchase can be justified.
Also, if there were ever any question about moving the data in place to
another host, Veritas makes that easy. I would guess it's possible
under SDS, but you'd have to find the right files to edit.

Since my primary concern is mirroring root disks, here's a very useful
information on how to do it with VxVM provided by Jed Dobson:
This is how its done with VxVM
format your disks with slice 3 & 4 free with 1 free sector available. Run
vx-install and select encapsulate boot disk. Call it bootdisk. After two
reboots run vxdiskadm. Initialize your mirror disk call it rootmir. Select
mirror disks from menu (item 6 I believe) and then input boot disk name as
source and rootmir as target. The mirror will then start.

Real easy less reboots than SDS. I don't like to mirror with VxVM, I will
use SDS since they are simple Solaris slices and I can revert back real,
real easy. Destroying plexes under VxVM is a little more complicated and
sometimes if you moved /opt (which can't exist on a boot disk - VxVM will
move it for you to the public region - takes some work to move back to
regular slices)

Also in a pinch you can boot from the cdrom and mount the slices as normal
with no issues.

Original question:
> Hello Gurus
> Could someone give or point me to a comparison between SDS and Veritas
> Volume Manager? I just need something like a list of basic advantages of
> one over the other.
> Any help is greatly appreciated.
> Thanks,
> Leonid Massarskiy

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