On 31/03/2012, at 9:21 AM, Doug Ambrisko wrote: > Jan Mikkelsen writes: > | I don't know what changes Sean did. Are they in 9.0-release, or do I > | need -stable after a certain point? I'm assuming I should be able to > | take src/sys/dev/mfi/... and src/usr.sbin/mfiutil/... from -current. > > It's in the SVN project/head_mfi repro. You can browse it via the web at: > http://svnweb.freebsd.org/base/projects/head_mfi/ > > It's not in -current yet. I'm working on the. I just did all the > merges to a look try and eye'd them over. Now doing a compile test > then I can check it into -current.
OK, will check it out. > | The performance is an interesting thing. The write performance I care > | about is ZFS raidz2 with 6 x JBOD disks (or 6 x single disk raid0) on > | this controller. The 9261 with a BBU performs well but obviously costs more. > > There will need to be clarification in the future. JBOD is not that > same as a single disk RAID. If I remember correctly, when doing some > JBOD testing version single disk RAID is that JBOD is slower. A > single disk RAID is faster since it can use the RAID. However, without > the battery then you risk losing data on power outage etc. Without the > battery then performance of a JBOD and single disk RAID should be able > the same. > > A real JBOD as shown by LSI's firmware etc. shows up as a /dev/mfisyspd<n> > entries. JBOD by LSI is a newer thing. Ok, interesting. I was told by the distributor that the 9240 supports JBOD mode, but the 9261 doesn't. I'm interested to test it out with ZFS. > > | I can see the BBU being important for controller based raid5, but I'm > | hoping that ZFS with JBOD will still perform well. I'm ignorant at this > | point, so that's why I'm trying it out. Do you have any experience or > | expectations with a 9240 being used in a setup like that? > > The battery or NVRAM doesn't matter on the RAID type being used since the > cache in NVRAM mode, says done whenever it has space in the cache for the > write. Eventually, it will hit the disk. Without the cache working in > this mode the write can't be acknowledged until the disk says done. So > performance suffers. With a single disk RAID you have been using the > cache. With RAID-5 it is important because a single update requires two writes and a failure in the window where one write has completed and one write has not could cause data corruption. I don't know whether the controller really handles this case. I guess I'm hopeful that ZFS will perform the function performed by the NVRAM on the controller. I can see how the controller in isolation is clearly slower without a BBU because it has to expose the higher layers to the disk latency. > Now you can force using the cache without NVRAM but you have to acknowledge > the risk of that. Yes, I understand the risk, and it is one I do not want to take. All the 9261s I have deployed have a BBU and go into write through mode if the battery has a problem. I think I need to test it in the context of ZFS and see how it works without controller NVRAM. Regards, Jan. _______________________________________________ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "freebsd-stable-unsubscr...@freebsd.org"
