On Oct 21, 2010, at 5:26 PM, Erik Trimble wrote: > On Thu, 2010-10-21 at 17:09 -0700, Richard Elling wrote: >> On Oct 21, 2010, at 6:19 AM, Eff Norwood wrote: >>> Let me frame this in the context specifically of VMWare ESXi 4.x. If I >>> create a zvol and give it to ESXi via iSCSI our experience has been that it >>> is very fast and guest response is excellent. If we use NFS without a zil >>> (we use DDRdrive X1==awesome) because VMWare uses sync (Stable = FSYNC) >>> writes NFS performance is not very good. Once we enable our zil >>> accelerator, NFS performance is approximately as fast as iSCSI. Enabling or >>> disabling the zil has no measurable impact on iSCSI performance for us. >>> >>> Does a zvol use the zil then or not? If it does, then iSCSI performance >>> seems like it should also be slower without a zil accelerator but it's not. >>> If it doesn't, then is it true that if the power goes off when I'm doing a >>> write to iSCSI and I have no battery backed HBA or RAID card I'll lose data? >> >> The risk here is not really different that that faced by normal disk drives >> which have >> nonvolatile buffers (eg virtually all HDDs and some SSDs). This is why >> applications >> can send cache flush commands when they need to ensure the data is on the >> media. >> -- richard >> > > I think you mean "volatile buffers", right? You'll lose data if you HD > or SSD has a volatile buffer (almost always DRAM chips with no battery > or supercapacitor).
Indeed... to quote someone (Erik) recently, (a) I'm not infallible. :-) -- richard -- OpenStorage Summit, October 25-27, Palo Alto, CA http://nexenta-summit2010.eventbrite.com USENIX LISA '10 Conference, November 7-12, San Jose, CA ZFS and performance consulting http://www.RichardElling.com _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
