On 5/25/2010 11:39 AM, Edward Ned Harvey wrote: >> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- >> boun...@opensolaris.org] On Behalf Of Kyle McDonald >> >> I've been thinking lately that I'm not sure I like the root pool being >> unprotected, but I can't afford to give up another drive bay. >> > I'm guessing you won't be able to use the USB thumbs as a boot device. But > that's just a guess. > No I've installed to an 8GB one on my laptop and booted from it. And this server offers USB drives as a boot option, I don't see why it wouldn't work. but I won't kow till I try it. > However, I see nothing wrong with mirroring your primary boot device to the > USB. At least in this case, if the OS drive fails, your system doesn't > crash. You're able to swap the OS drive and restore your OS mirror. > > True. If nothing else I may do at least that. > >> That led me to wonder whether partitioning out 8 or 12 GB on a 32GB >> thumb drive would be beneficial as an slog?? >> > I think the only way to find out is to measure it. I do have an educated > guess though. I don't think, even the fastest USB flash drives are able to > work quickly, with significantly low latency. Based on measurements I made > years ago, so again I emphasize, only way to find out is to test it. > > Yes I guess I"ll have to try some benchmarks. The thing that got me thinking was that many of these drives support a windows feature called 'Ready boost' - which I think is just windows swapping to the USB drive instead of HD - but Windows does a performance test on the device to seee it's fast enough. I thought maybe if it's faster to swap to than a HD it might be faster for an SLOG too.
But you're right the only way to know is to measure it. > One thing you could check, which does get you a lot of mileage for "free" > is: Make sure your HBA has a BBU, and enable the WriteBack. In my > measurements, this gains about 75% of the benefit that log devices would > give you. > > My HBA's have 256MB of BBC. And it's enabled on all 6 drives, so that should help. However I may have hit a bug inthe 'isp' driver (still have to debug and see if that's the root cause) and I may need to yank the RAID enabler, and go back to straight SCSI. -Kyle _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
