On Tue, 3 Jun 2008, Niclas Sodergard wrote: > > Thanks for your fast reply. I've read your white paper (as well as the > email thread that it originated from) at I must say it is very good, > nice work! A few questions: > > 1. Is there a difference between disabling the cache nvsync and run > ZFS with nocacheflush?
Yes. The firmware cache tweak provided by Sun support still uses the RAID controller cache but has the RAID controller report that the data is synced as soon as the data is in the controller's cache rather than once it is on disk. That means the data is still securely stored (to the limit of cache RAM batteries). If you tell ZFS not to flush data when requested, then there can be data loss, and particularly problems for NFS clients if the server reboots without the data the client recently wrote. > 2. Why do you have separate storage pools for each disk? Would you get > the same result of having 12 different virtual disks and share the > same pool? With a storage pool for each disk then the ZFS write queue for the disk is tied to actual hardware. With virtual disks sharing the same pool there is no telling where the data is actually going. For example, maybe all 12 write queues are pointed at the same disk and then performance would really suck (e.g. 12MB/s). There is also the issue of what to do when a disk is replaced. Unless you are using redundundancy in the RAID array, you would not be able to replace a failed disk since ZFS does not know what is on the physical disk. If you use the RAID in the array for fault tolerance (rather than ZFS RAID) then you will want to create several pools and export each pool as a LUN for use by ZFS. The 2540 has a 4 disk RAID-5 config with 128k blocks that it advertizes as being good for ZFS. Keep in mind that if you use several LUNs in a load-share configuration that the system may panic if one of those LUNs fails for some reason and the other LUNs are still alive. > You're absolutely right but 12MB/s is a very low number IMHO. But it seems to be the limit of what an el-cheapo USB drive can offer. :-) Make sure that your fiber channel connections are working right. Are you sure that they are not continually resetting or experiencing huge numbers of errors? Bob ====================================== Bob Friesenhahn [EMAIL PROTECTED], http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/ _______________________________________________ storage-discuss mailing list [email protected] http://mail.opensolaris.org/mailman/listinfo/storage-discuss
