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 -- 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
