growse.com

I write things here.

I'm on Keybase.

Last seen floating around near Horsforth. 68,277.77 miles this year.

More Fibre Channel Nonsense

Fibre Channel lives on! Following from a brief dabble in the past with using Fibre Channel, I decided that it was once again the time to see if I could make it work.

This was was all prompted by the replacement of my old HP Microserver N40L with the much newer G8 model. This broadly does the same thing, but lets you have more memory and better CPUs. Useful for running ZFS on Linux.

So, I was pleasantly surprised to see that a tiny budget lets you buy 4Gb FC kit, rather than the 2G stuff I’d bought a few years ago. I picked up a couple of QLogic QLE 2460 cards and re-used the MM fibre that I had from before.

The main challenge was getting to play nicely with Linux. Before, I had used Solaris which has much better out-of-the-box support for FC targets and integrating it with ZFS. On Linux, SCST seemed to be the right solution. I was running Ubuntu 15.10, and initially found that someone had made some SCST Packages on a PPA. Adding this and then simply doing apt install scst-dkms was all that was needed to get up and running. Adding an FC target was as simple as creating a zfs volume (zfs create -V 1T netank/vols/bumpvol1) and then adding the configuration into the scst configuration file:

HANDLER vdisk_blockio {
        DEVICE bumpvol1 {
            filename /dev/zvol/newtank/vols/bumpvol1
            nv_cache 0
        }
}

TARGET_DRIVER qla2x00t {
        TARGET 21:00:00:e0:8b:9b:bd:d5 {
                enabled 1
                LUN 0 bumpvol1
        }
}

You’ve got to blacklist the kernel-supplied qla2xxx driver and use the qla2x00t instead. It’s also important to set sync=always on the ZFS volume, and use nv_cache 0 on the SCST side. A ZIL is apparently recommended to improve performance. There’s a good discussion on the SCST dev mailing list about this.

This all trundled along great, until I had to reboot the box. When it came back, SCST wouldn’t start. I narrowed it down to the kernel having been updated to v4.2.0-30, for which the scst-dkms package had failed to compile the relevant modules. It seemed that I had to either roll back the kernel, or find a different solution. Thankfully, the detailed instructions on how to build SCST from source with the qla2x00t module , while a little daunting, worked great. Just need to remember to re-build these whenever there’s a kernel upgrade.

Next steps are to pick up an absurdly cheap SSD and try and use that as a ZIL device to improve performance. I think I’ve run out of SATA slots on the Microserver though, so will have to come up with something.

Also, I bought a new piccolo. It squeaks pleasingly.

comments powered by Disqus