> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- > boun...@opensolaris.org] On Behalf Of Paul Kraus > > I am looking for references of folks using ZFS with either NFS > or iSCSI as the backing store for VMware (4.x) backing store for > virtual machines.
Since I had ulterior motives to test this, I spent a lot of time today working on this anyway. So I figured I might as well post some results here: #1 If there's any performance difference between iscsi vs nfs, it was undetectable to me. If there's any difference at all, nfs might be faster in some cases. #2 I previously speculated that performance of iscsi would outperform nfs, because I thought vmware would create a file on NFS and then format that file with vmfs3, thus doubling filesystem overhead. I was wrong. In reality, ESXi uses the NFS datastore "raw." Meaning, if you create some new VM named "junk" with associated disks "junk.vmdk" etc, then those files are created inside the NFS file server just like any other normal files. There is no vmfs3 overhead in between. #3 I previously believed that vmfs3 was able to handle sparse files amazingly well, like, when you create a new vmdk, it appears almost instantly regardless of size, and I believed you could copy sparse vmdk's efficiently, not needing to read all the sparse consecutive zeroes. I was wrong. In reality, vmfs3 doesn't seem to have any advantage over *any* other filesystems (ntfs, ext3, hfs+, etc) to create and occupy disk space with the sparse files. They do not copy efficiently. I found that copying a large sparse vmdk file, for all intents and purposes, works just as well inside vmfs3 as it does in nfs. Those things being said ... I couldn't find one reason at all in favor of iscsi over nfs. Except, perhaps, the authentication which may or may not be stronger security than NFS in a less-than-trusted LAN. iscsi requires more work to setup. iscsi has more restrictions on it - You have to choose a size, and can't expand it. It's formatted vmfs3, so you cannot see the contents in any way other than mounting it in esx. I could not find even one thing, to promote iscsi over nfs. Although it seems unlikely, if you wanted to disable ZIL instead of buying log devices on the ZFS host, you can easily do this for NFS, and I'm not aware of any way to do it with iscsi. Maybe you can, I don't know. I mean ... It wasn't like Mike Tyson beating up a little kid, but it was like a grown-up beating up an adolescent. ;-) Extremely one-sided as far as I can tell. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
