Thanks for clarification Niels, but I am not yet clear if the NFS used to mount GlusterFS is the same as stock NFS in the kernel tree (which uses FS-Cache)? My other question is that does NFS client of GlusterFS commits and blocks for each write(not flush, just a write)? or does it use "weak cache consistency model" allowing some buffering for writes.
Thanks, On Tue, Apr 28, 2015 at 7:29 AM, Niels de Vos <[email protected]> wrote: > On Mon, Apr 27, 2015 at 02:56:14PM -0400, Behrooz Shafiee wrote: > > Hello all, > > > > I am a graduate student at University of Waterloo and working on > > filesystem. I have two questions about GlusterFS that I will appreciate > if > > anyone can comment about. > > > > First, does GlusterFS FUSE client bypass Linux page cache mechanism(mount > > with -o direct_io)? I have a machine with 64 GB of memory and when I > write > > a about 30GB of data into that machine (less than available memory) and > > read it again, I see the reads are server through network, even though > > those file could/are in the Linux page cache memory. It seems that's the > > case both for NFS and FUSE clients. > > Direct IO is intended to not use caches where possible. What you > describe above is the expected behaviour. You can find more details in > 'man 2 open' for the O_DIRECT flag. > > The Linux kernel has many tunables for the page cache. You can find many > of them under /proc/sys/vm/ , some are documented in 'man 5 proc'. > > > My second question is about FS-Cache and if GlusterFS does inode tree > cache > > on its FUSE clients or not. I know it exist in NFS but is the NFS client > of > > GlusterFS same as regular NFS? > > FS-Cache is a client-side option for some filesystems. The Linux kernel > supports FS-Cache for its NFS-client. Some work has been done to add > support for FS-Cache to FUSE, but that never became stable enough to get > included in the upstream Linux kernel. Vimal Kumar did most of the work > for that, and had a proof-of-concept. It will need updating for the > current kernel version and some stability fixes. One of the email > threads is here: > > http://thread.gmane.org/gmane.comp.file-systems.gluster.devel/7877 > > Vimal was planning to continue working on this, and your email is a > great reminder to get a status update from him. > > Cheers, > Niels > -- Behrooz
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