Sun's Volume Manager

Peter Baer Galvin

It used to be Solstice DiskSuite and Solaris Disk Suite. Now it's Solaris Volume Manager. Was the name changed to highlight new functionality, or to protect the guilty? This month, the Solaris Corner takes it for a spin to determine which is the case.

Overview

As with the past couple of Solaris Companion columns, this one addresses a new Solaris 9 feature. This month, I'll examine Solaris Volume Manager (SVM) and take a close look at its features, problems, and a field trial. Does SVM give Veritas Volume Manager some competition on large disk-space machines? Probably not. But it does have sufficient utility to be used on small systems, as did DiskSuite, and even on mid-sized machines with moderate disk space. In the remainder of this column, I'll look at the features and functions of SVM, walk through an implementation, and evaluate the final results.

Features

SVM is now a full member of the Solaris product. It is installed by default, not separately. Its integration is a welcome relief to those who need volume management. In the old days (Solaris 8 and below), any disk management had to be removed from any system disks before upgrades could be performed, and had to be re-implemented after the upgrade. With SVM, upgrades are supposed to be knowledgeable of it and not require it to get special treatment.

Other important changes to SVM were long in coming, but are still welcome. It now has a concept of virtual disks, in which it dices a physical disk into N virtual disks (which are variously called "volumes" and "metadevices"). "N" can be 8192 at the extreme, but it is limited by default to 128. SVM used to be limited to the standard eight partitions. A volume can be "sliced" to contain its own virtual partitions. SVM also has the idea of diskgroups (called "disk sets"). This is a set of disks that travels together and cannot be split between systems. This is useful for clustering, for example, where all of the disks involved in an Oracle instance would need to be mounted together on one machine.

Another nice change is that volume names are stored within the volumes. A disk moved from one physical slot to another will not be mistaken for the disk that used to occupy that slot, resulting in data loss or worse (that is, job loss). Rather, the system will read the volume information, determine what is on the disk, and reinitiate RAID protection or whatever is appropriate.

SVM also retains some old features. A hot spare pool provides slices to be used as replacements for failed RAID-protected slices. SVM supports the usual RAID suspects -- RAID 0, 1, and 5. It is flexible enough to allow you to build RAID 0+1 (stripe and then mirror) and RAID 1+0 (mirror and then stripe) volumes (although I did not test these). It still uses state databases and replicas to maintain the state of the entire configuration. It still provides "transaction volumes" for logging UFS metadata changes, but that has been superceded by the logging that is now built into UFS.

The documents regarding SVM are encompassing and useful. They provide not only "how to" information, but also guidelines on the best ways to use RAID, best disk layouts, naming conventions to use, best use of file systems, performance optimization, and so on.

Installation

The test system is a SunBlade 100 with two internal IDE disks. The system is generic, running unpatched Solaris 9. Before using SVM, I was a good worker bee and read through the Solaris 9 Runtime Issues release notes. It was disappointing to see six separate issues having to do with SVM. All of the issues seem avoidable with planning, so if you are planning on using S9 SVM, I recommend reading up on these issues. Another disappointment is Sun's choice to call this facility Solaris Volume Manager. There is already the Veritas Volume Manager (VXVM). Sun also OEM's this facility as the Sun StorEdge Volume Manager (SEVM). Great attention must now be paid when looking at bug reports and patches to ensure that they are addressing the correct volume manager. Many bug and patch reports simply talk of "volume manager" and must be read in detail to see exactly to what they are referring. That said, there did not seem to be any SVM-specific patches available at the time of this writing (August 2002). DiskSuite seemed like a fine name to me...

As mentioned, SVM is installed by default with the full Solaris package set. Management of SVM is either by the "Enhanced Storage tool" within the Sun Management Console or via the command line. The documentation warns not to try to use both methods at once or bad things could happen. For this test, I used the GUI, just to be different. It is started via the command /usr/sbin/smc. Navigating through "This Computer" to "storage" and then "enhanced storage" leads to the screen shown in Figure 1.

As with DiskSuite, the first step with SVM on a new machine is to create state database replicas. Choosing the replica tool in SMC, then using the action->create replicas menu selection allowed creation. Unfortunately, the root disk on the test system was fully partitioned, with no unused disk space that could be used by SVM. When installing the system, I performed a custom disk layout, so it is unclear whether the new default disk layout would have left space free for SVM to use. To remedy the situation, I carved out a 50-MB partition from the swap space. First, I did a swap -d of the root disk swap partition to un-allocate it, allowing it to be repartitioned. Second, I used format to add a slice 5 to the system, made from the last 50 MB of slice 0 (swap). Labeling the disk made it happen. (At that point my Open Windows session exited -- possibly because I needed space to page to but had no swap space allocated. I had further stability problems with OpenWindows, and decided to install the current Solaris 9 patch cluster.)

While I was in a partitioning mood, I partitioned my second disk the same way. It was unclear whether SMC and SVM would have chosen to duplicate the root disk layout, so I forced the issue. Next, I chose to create replicas on slice 5 of the two disks. I put two replicas per slice, as a minimum of three slices is required. Obviously, three disks with one replica each would have been optimal. I enabled "show commands" within SMC, and it obliged by showing what it was about to do.

Determining how to mirror an existing file system partition was more of a challenge. The SVM documentation provides both GUI and command-line directions for mirroring a partition that cannot be unmounted (e.g., the root disk partitions). Unfortunately, following the instructions for the GUI method failed, because it reported that the partition was mounted and did not give an option for using a mounted partition. Thus, the GUI had to be abandoned and the command line used:

metainit -f d1 1 1 c0t0d0s0 -- Create a concat RAID 0 slice from the existing slice.

metainit d2 1 1 c0t2d0s0 -- Find the equivalent unused slice on the mirror disk and make it a concat RAID 0 as well.

metainit d0 -m d1 -- Create a one-way mirror from the existing RAID 0.

metaroot d0 -- Change /etc/vfstab and /etc/system to use the new mirror (reboot the system).

metattach d0 d2 -- Mirror the existing RAID 0 one-way mirror to the second disk.

metastat -- To check SVM status and assure commands executed properly.

Note that for complete functionality, you must change the eeprom to use the d2 slice as the alternate boot device. In this way, if the primary root slice failed, the secondary would be used automatically after a reboot.

As an experiment, I next performed the concat RAID 0 creation on swap and /export/home via the command line (the metainit -f commands that were not executable via the GUI). I then used the GUI to create the mirror pairs. The wizard use was a bit tedious, but selecting the correct options was straightforward. It helped to have a list of the metadevice names and their related partitions -- to help assure that a blank disk was not mirrored to its filesystem-containing counterpart, for example. On the surface, this method worked correctly. However, the GUI did not update /etc/vfstab to tell the system to use the new mirror devices rather than the original partitions. Making this change and rebooting the system resulted in a fully mirrored root disk implementation. The final GUI view is shown in Figure 2. The final /etc/vfstab is shown in Figure 3.

Conclusions

SVM appears to be a nice leap forward from the old DiskSuite. Inclusion by default on a system makes the facility more seamless. Awareness of SVM by Solaris installation tools should allow much simpler systems administration of SVM-managed disks. SVM is easy to get started with (especially with the available GUI), but root disk mirroring is still a manual and detail-oriented task. Performing non-root-disk tasks should be easier. In my simple testing, it worked and performed well.

Extensive testing within your environment would be a great step toward full use of SVM on your systems. The soft volume feature adds a lot of flexibility and is worth exploring. For example, you could take a RAID 1 set, and create N soft partitions on it, one for each user on the system. Should a user run out of space, you could expand the soft partition to make more available.

Overall, SVM moves Sun's disk management tools from the realm of small-number-of-disk systems to those with a moderate number of disks. I would still hesitate to use it for terabytes of SAN-attached storage, but it could handle gigabytes of locally attached storage and save money by replacing Veritas Volume Manager in those instances.

Good Book Alert

Well, O'Reilly has done it again with the new edition of The Networking CD Bookshelf. Version 2.0 contains a CD that includes the full contents of seven O'Reilly & Associates books: TCP/IP Network Administration 3rd ed; Managing NFS and NIS 2nd ed; Network Troubleshooting Tools; SSH, the Secure Shell: The Definitive Guide; Essential SNMP; DNS and Bind 4th ed; and Building Internet Firewalls 2nd ed. I find the books on Firewalls and NFS especially good, with useful reference material in the others. The "Book" also includes one printed book, TCP/IP Network Administration. My guess is that the printed book is the best seller of this lot, but that is just a guess. The books are all in HTML format with embedded images. All are accessible via a browser home page showing all the books and providing a search feature that will search all the books via one button. Books can be searched separately as well. I found no browser-related issues, as the contents worked fine in MS Explorer, as well as Mozilla 1.0.

The cost is on the high side for a book ($119.95 US list), but considering all the content and the utility of having the contents electronically and searchable, it's a bargain. The only potential downside is the license agreement that essentially allows access to the contents by only one user. The contents cannot be centrally located and remotely accessed by multiple people, for example, without buying more licenses. For personal use, however, I loaded a copy of the contents on my home Linux server, which I can access remotely, on my home network, or via my wireless network. I also put a copy on my laptop, and even onto the 1-GB CF drive I use on my PDA. The content is only 50 MB, so this is quite reasonable. It's nice to know that I have all that great information available no matter when I am. Overall, The Networking CD Bookshelf 2.0 is a reasonable price for a great set of books provided in the most useable manner possible. Highly recommended.

Peter Baer Galvin (http://www.petergalvin.org) is the Chief Technologist for Corporate Technologies (www.cptech.com), a premier systems integrator and VAR. Before that, Peter was the systems manager for Brown University's Computer Science Department. He has written articles for Byte and other magazines, and previously wrote Pete's Wicked World, the security column, and Pete's Super Systems, the systems management column for Unix Insider (http://www.unixinsider.com). Peter is coauthor of the Operating Systems Concepts and Applied Operating Systems Concepts textbooks. As a consultant and trainer, Peter has taught tutorials and given talks on security and systems administration worldwide.