[ Wish there was a generic, active Linux "storage" mailing list out there -- something other than the kernel lists I mean ]
To frame the discussion, we use VMware ESX (vSphere) quite a bit with NFS datastores. Often times with NetApp, but lately, more often with Solaris 10 + ZFS + SSD's for ZIL (intent log or write cache).
The ZIL lets us use synchronous writes (safer) without the normal delay. Were we to try and get the same level of performance with Linux, we'd need to use async mode for our NFS shares -- and we'd lose some reliability.
However, given the latest rumblings and ruminations about Oracle potentially no longer selling entitlements for Solaris 10 on non-Sun hardware -- and then turning around and no longer allowing you to run Solaris 10 "freely", we're left with either OpenSolaris or looking at Linux again (we run Solaris 10 on Silicon Mechanics hardware).
My question is, what are the various options for getting NFS in "sync" mode to run fast on Linux?
Obviously we can buy a really nice disk controller with lots of cache, but I'm thinking more at the filesystem, volume manager or block driver layer. Is there a way to shunt write requests to a quicker medium like an SLC-based SSD (or NVRAM)?
I don't see a way to do this with LVM, ext3/ext4 or even xfs... maybe btrfs will have some options along this line down the road, but that's tomorrow and not today.
So is a beefy disk controller our best option? Even using our 3Ware 9650's w/ BBU so we can enable write-back doesn't seem to give us as good of write performance via NFS as ZFS+ZIL-on-SSD does...
Ray