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Disks, Solaris, ZFS, Fibre Channel, COMSTAR, Crumpets and Butter.

I did a thing.

Because I’m moving house (yes yes, old news, I know) one of the things that I’m looking to downsize on is the amount of space my dvd collection takes up in my living room. At the moment, it’s “far too much” and in the new house, it’s bordering on “ridiculous”. So I came up with a plan: Rip each dvd entirely to disk, plug it into XBMC and enjoy the vast amount of free space I just created.

However, there’s a problem. My current storage box thingie is too small, and doesn’t have any room for any more capacity. There was only one option: build a new storage box thingie!

I had grand plans this time. I had a fairly hefty requirements list around availability, redundancy, performance and capacity, so in short I needed something that worked, worked well and had the ability to grow bigger in the future. ZFS was the obvious choice. I know that previously I’ve ranted about Oracle and how they’re potentially quite evil, but on balance, ZFS is too awesome to miss. It comes with a big dollop of Oracle-shaped risk, but for this application that’s a risk I’m prepared to take.

Hardware first: I bought one of these. If the link’s dead, it’s a 4U rackmount 20 bay SAS hotswap case. Not cheap, but it turns out that hotswap rackmount cases generally aren’t. Into this I stuck an old SMP motherboard with 2 AMD Opteron 265s in it, which I just happened to have lying around. I also bought a couple of Q-Logic QLA2340 2GB fibre cards (£20 each on ebay). I also had 8 500GB disks lying around, so that was a good start.

Software: I like Solaris, but OpenSolaris seems to be in a bit of limbo at the moment. In the spirit of throwing caution to the wind, I plumped with Nexenta, which is basically OpenSolaris with a GNU userland. So it feels GNU-y, but is actually Solaris. I’ve used it before and it’s fairly solid.

So, I started to set everything up. Predictably, I hit problems instantly. I guess I should be pleasantly surprised that a bunch of hardware that’s been collecting dust for the past 3 years should actually work, but it did. At first. The problems came with the software. The Nexenta installation went without a hitch, but when it next booted, the Solaris kernel promptly told me that a number of AMD Errata hadn’t been corrected in the BIOS, before promptly giving me a kernel panic with:

panic[cpu2]/thread=fec203a0: Too many lgrps for platform (4)

Great.

Solaris’ recommendation was that I update the BIOS, which might be tricky given that Iwill went out of business 4 years ago. They also recommended that I turn NUMA off in the BIOS, which wasn’t an option that I was given. It turns out there is no solution to this, and with Iwill not existing and the open source Solaris kernel in a current state of limbo, not likely to be a solution either. Luckily, the system boots after going through a panic/reboot cycle about 10 times. No idea what’s going on there.

So I set up the zpool with the 8 disks in a mirrored config and all goes well. Next step is to expose a zvol as a FC lun through the QLogic card. This didn’t work. I spent several days reading, configuring, reading, shouting, writing and more reading, all of which culminated in this post on ServerFault (I earned the ‘mothball’ badge for that!). I came to a simple conclusion: you can’t make a 2GB QLogic card a FC target on Solaris. Can’t be done. Impossible. You either need a QLogic 4Gb card (£200 on ebay) or an Emulex card (£20 on ebay). I went with Emulex - specifically an LP10000DC dual-port thingie.

A few days later, this turned up, and worked. Properly. You have to set a target-mode=1 setting in the /kernel/drv/emlxs.conf and make sure the firmware is up to date, but other than that, smoothness. I’m properly impressed with COMSTAR too - the configuration required to get something up and running is so minimal:

$ zfs create -V 500g tank/comstar/target1
$ sbdadm create-lu /dev/zvol/rdsk/tank/comstar/target1
$ stmfadm add-view

And that’s it. You can get more complex with host groups and target groups, but that’s not really necessary for something like this. What’s more, because it’s ZFS, you get built-in SMB and NFS sharing, deduplication, compression, fault tolerance etc. all for free. That said, I’d recommend you turn dedup off for zvols, unless you want write speeds of 2MB/s. Works perfectly fine for regular ZFS filesystems though.

So, for several thousand pounds less than what EMC/NetApp/whoever would have charged, I’ve got a decent NAS/SAN box at home that does what I need it to do, mostly. There’s still problems - I need a new motherboard at some point to get around the kernel panic issue, and the write performance on zvols through COMSTAR is weirdly bursty.

I guess I’d suggest that if you want something that works first time without any shouting, spend a lot of money. If you like a lot of head-scratching, shouting, reading and a general sense of achievement when it does all work, build it yourself.

(X-case RM420)