If I add a disk to a volume, what will it do to performance, and for how long? I don't mean long-range gains from having the data spread over more spindles, I mean what immediate impact will it have on current NFS clients. Will it just be a temporary increase in CPU as it spreads the data or will it freeze for some period of time, and if so for how long?
Frank,
Adding a disk into a volume will cause increased CPU and I/O load for < 10 minutes while data is copied over. It won't freeze the system or do anything disasterous like that.
If you're only running at a couple of hundred nfs ops/sec, you don't really have anything to worry about unless you have client applications which are extremely sensitive to filesystem performance (in which case you probably shouldn't be using nfs anyway). In fact, it's quite likely that your clients aren't going to notice anything while the disk is being added to your volume.
Nick