On Jul 09, 2007 07:08 -0700, Zhe Zhang wrote: > Thanks for the reply. What about read-ahead then? Is it the same > as caching, and is performed on the client side only?
The readahead is only on the client side, since most uses of Lustre have such a high load on the server that doing readahead on the server is a net loss of performance. The amount of client readahead is tuned on the client via /proc/fs/lustre/llite/*/max_read_ahead_mb. There is a second tunable /proc/fs/lustre/llite/*/max_read_ahead_whole_mb, which is the size of a file (in MB, or fraction thereof) below which the whole file will be read into the client cache regardless of the IO pattern. > ----- Original Message ---- > From: Andreas Dilger <[EMAIL PROTECTED]> > To: Zhe Zhang <[EMAIL PROTECTED]> > Cc: [email protected] > Sent: Tuesday, July 3, 2007 5:54:49 PM > Subject: Re: [Lustre-devel] Lustre Server Caching > > On Jul 03, 2007 06:41 -0700, Zhe Zhang wrote: > > I have a question about the caching policy Lustre uses on > > the server side. I'm using 1.4.7 and my current setting > > is 1 MDS, 3 OST and 2 clients. My experience is that if > > client 1 first fetches a file "foo" from Lustre to its > > own /tmp directory and client 2 tries to fetch "foo" later, > > client 2 will get the file faster. I wonder if Lustre is > > using caching on the server side. I mean, data server, not > > MDS. I searched this mail list and did not get clear clue. > > Can anybody tell me if a Lustre server will save accessed > > data in its memory or not? It is quite important in the > > performance analysis of our research. > > Lustre does NO data caching on the server. However, it DOES do caching > of the file metadata, so this might speed the second access to the file. > > Cheers, Andreas > -- > Andreas Dilger > Principal Software Engineer > Cluster File Systems, Inc. Cheers, Andreas -- Andreas Dilger Principal Software Engineer Cluster File Systems, Inc. _______________________________________________ Lustre-devel mailing list [email protected] https://mail.clusterfs.com/mailman/listinfo/lustre-devel
