On Tue, May 10, 2005 at 08:12:51PM +0100, David Howells wrote: > > Steve Dickson <SteveD@xxxxxxxxxx> wrote: > > > But the real saving, imho, is the fact those reads were measured after the > > filesystem was umount then remounted. So system wise, there should be some > > gain due to the fact that NFS is not using the network.... > > I tested md5sum read speed also. My testbox is a dual 200MHz PPro. It's got > 128MB of RAM. I've got a 100MB file on the NFS server for it to read. > > No Cache: ~14s > Cold Cache: ~15s > Warm Cache: ~2s > > Now these numbers are approximate because they're from memory. > > Note that a cold cache is worse than no cache because CacheFS (a) has to check > the disk before NFS goes to the server, and (b) has to journal the allocations > of new data blocks. It may also have to wait whilst pages are written to disk > before it can get new ones rather than just dropping them (100MB is big enough > wrt 128MB that this will happen) and 100MB is sufficient to cause it to start > using single- and double-indirection pointers to find its blocks on disk, > though these are cached in the page cache. How big was the cachefs filesystem? Now try reading a 1GB file over nfs.. I have found (with openafs), that I either need a really small cache, or a really big one.. The bigger the openafs cache gets, the slower it goes. The only place i run with a > 1GB openafs cache is on an imap server that has an 8gb cache for maildirs.
