In (modest) praise of Solaris DiskSuite

October 27, 2006

Now that I've worked with it for a while, I have to admit that Solaris DiskSuite is actually pretty neat. Since I've been dissatisfied with most of the other bits of Solaris, this came as something of a surprise to me.

(Solaris DiskSuite is Sun's version of software RAID, for those who have not encountered it before.)

There's nothing revolutionary in DiskSuite; it's just well integrated. This is really the advantage of a single-source vendor; Linux can probably duplicate almost all of DiskSuite's functionality, but you'd have to glue all the bits together, which is a pain.

(I say 'almost all' because Linux is not as smart as DiskSuite for peeling parts of mirrors off and then putting them back on. Linux forces a full mirror resync, while DiskSuite appears to keep track of what got written to while the submirror was offline and only updates that, which is much faster.)

This is partly a social advantage more than a technical one, because Sun is in a position to say internally 'we will do it this way'. By contrast, if the Linux software RAID people (for example) picked one of the various high availability systems to work with it would be a pretty divisive thing and unlikely to be well accepted. This is good for forcing all of the Linux HA systems to compete on technical appeal instead of how well they can sell themselves to someone in a position to pick a winner, but bad for getting a generally accepted and well integrated HA system for NFS fileserving.

I've found that one advantage of getting significantly involved with DiskSuite is that it gives me a better appreciation of the good and bad bits of both DiskSuite and Linux software RAID. Using multiple implementations of the same idea is useful to give you a deeper view of it, and this time has been no exception.

(This is not to say that DiskSuite is perfect. There's certainly a number of Linux software RAID features that I really wish DiskSuite had stolen, and that's not even touching LVM.)

All of this does make me really curious about Solaris 10's ZFS stuff, which is presumably (in part) the follow-on to DiskSuite. Unfortunately we're unlikely to run Solaris 10 any time soon, so I will probably not get to play around with it in the near future.


Comments on this page:

From 24.98.83.96 at 2006-10-28 20:11:20:

Disksuite (also referred to as Solaris Volume Manager) is definitely nifty, and it sure beats the socks off the Linux equivalent (if you didn't have to use both MD and LVM to mirror and grow volumes, it wouldn't be so bad). Which features do you think Disksuite is missing? Sun finally added vanity name support, which allows you to give metadevices arbitrary names (I never quite understood why they required you to name things dXXX). This was the only feature I thought made SVM incomplete.

- Ryan

By cks at 2006-10-29 00:09:46:

Here's a random set of things about the Solaris 8 version of DiskSuite that I find surprising and/or less than perfect:

  • you cannot abort a DiskSuite (sub)mirror resync in software.
  • the physical partitions that make up DiskSuite devices are not self-identifying. Instead, DiskSuite keeps a (possibly replicated) external database of what's what and so on.
  • perhaps because of the above, you apparently cannot easily change around the physical device identifiers of DiskSuite devices; if c0t3d0s1 changes to c1t3d0s1 because of some hardware shuffles, DiskSuite will apparently not just pick up and go.
  • you cannot have more than four-way mirroring.
  • you cannot have stripes of mirrors, which means you cannot build a RAID-10 setup. (You cannot have a mirror of mirrors either.)

Since you need a full mirror if you want to offline a submirror to snapshot it for backups, the last issue can really bite. For example, we had a situation where the ideal setup would have been a mirror of a stripe of plain disks and a stripe of RAID-1 pairs.

(I am excluding Linux LVM features from this, because I think it would be an unfair comparison; DiskSuite is software RAID, not a volume manager.)

Written on 27 October 2006.
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