On Nov 28, 2007 11:11 PM, Chris Johnson <johnson@xxxxxxxxxxxxxxxxxxx> wrote: > On Wed, 28 Nov 2007, Kevan Benson wrote: > > > Chris Johnson wrote: > >> Hi again. > >> > >> I've scaled everything way back as was suggested. I'm also using > >> a dd file read as a test rather than iozone. I have one brick on the > >> server mounted on the client, that's it. Using time dd I get between > >> 260 to 285 MS to read a 24 MB file. Doing the same thing with NFS I > >> get about 20 to 30 MS less but I can live with that. OK, noted. I am guessing this is because of user space overhead. > >> > >> I tried with and without io-threads on the server end. No > >> noticable change either way. I've read with io-threads is supposed to > >> do. I had 8 threads defined. What does it do and does it make a > >> different which side it's on, client or server? > > > > io-threads is supposed to speed up serving of files when multiple files are > > requested at the same time (so dd won't trigger any benefits from it at all, > > being a single request). I.e. In situations on the server where it would be > > blocking on new requests until finished with the current request, io-threads > > allows another thread to handle the request for better response and > > performance (at least that's how I understand it). Correct. When multiple processes request for multiple files, performance gain will be significant. > > > > As another email a few days ago stated, io-threads on the client side will > > have little or no effect. I had observed that client side io-threads also improves response time. > > Ah ha! Ok, tnx. > > > > >> I also tried the io-cache on the client side. MAN does that > >> work. I had a 256 MB cache defind. A reread of my 24 MB file took 72 > >> MS. I don't think it even bothered with the server much. I need to > >> try that on the server. Might help if a bunch of computer nodes > >> hammer on the same file at the same time. > > > > Careful with io-cache and io-threads together, depending on where you define > > it (I think), the cache is per-thread. so if you have 8 threads and a 256 MB > > cache defined, be prepared for 2 GB of cache use... > > No, If you define one io-cache translator there is only one cache. All the threads will refer to the same io-cache translator with which it is associated Krishna
