Kyle McDonald wrote: > Richard Elling wrote: > >> Nick wrote: >> >> >>> I have been tasked with putting together a storage solution for use in a >>> virtualization setup, serving NFS, CIFS, and iSCSI, over GigE. I've >>> inherited a few components to work with: >>> >>> x86 dual core server , 512MB LSI-8888ELP RAID card >>> 12 x 300GB 15Krpm SAS disks & array >>> 2GB Flash to IDE "disk"/adaptor. >>> >>> The system will be serving virtual hard disks to a range of vmware systems >>> connected by GigE, running enterprise workloads that are impossible to >>> predict at this point. >>> >>> Using the RAID cards capability for RAID6 sounds attractive? >>> >>> >>> >> Assuming the card works well with Solaris, this sounds like a >> reasonable solution. >> >> > Another solution, might be to create several (12?) single disk RAID0 > LUNs, and let ZFS do your redundancy across them. The HW RAID card will > still give each RAID0 LUN the advantages of the NVRAM cache, but with > ZFS (RAIDZ2?) doing the redundancy, then ZFS will be able to recover > from more situations (at least as I understand it.) > >> >> >>> Using the Flash RAM for the ZIL? >>> >>> >>> >> I'm not sure why you would want to do this. Just carve off a >> LUN or slice on the RAID card and use its NVRAM cache. >> A consumer class flash "disk" will be slower. >> >> >> > This is an interesting observation. > > Will a separate LUN or slice on the RAID card perform better not > separateing out the ZIL at all? >
Yes. You want to avoid mixing the ZIL iops with the regular data iops with contention at the LUN. This is no different than separating redo logs for databases. > I'm trying to imagine how this works. How does the behavior of internal > ZIL differ from the behaivor of the external ZIL? Given that they'd be > sharing the same drives in this case how will it help performance? > > ZIL log can be considered a write-only workload. The only time you read the ZIL is on an unscheduled reboot. > I'm thinking of a comparison of an internal ZIL on a RAIDZ(2?) of 12 > single drive RAID0 LUNs, vs. either A) 12 RAID0 LUNs made from 95%+ of > the disks plus a RAID (5,6,10?,Z?,Z2?, something else?) LUN made from > the remaining space on the 12 disks, or 11 single drive RAID0 LUNS plus > a single drive RAID0 LUN for the ZIL. > > I can see where B might be an improvement. but no redundancy for the > ZIL, and un;ess it's a smaller disk, probably wastes space. > > A offers redundancy in the ZIL, and many spindles to use, but I'd image > the heads would be thrashing between the ZIL portion of the disk and the > ZFS portion? wouldn't that hurt performance? > The ZIL log should be a mostly sequential write workload which will likely be coalesced at least once along the way. It is also latency sensitive, which is why the NVRAM cache is a good thing. Beyond those simple observations, it is not clear which of the multitude of possible configurations will be best. Let us know what you find. -- richard _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
