Ray Van Dolson wrote:

On Tue, Dec 01, 2009 at 05:09:31PM -0600, Paul Berger wrote:

...

Has anybody got persistent NFS caching to work after 5.3 update removed the tech preview?

I have cachesfilesd installed & running and using nfs-utils with fsc patched back in but it appears to not be working, any pointers?

I can't find the link, but I thought the kernel components required for FS-Cache to function were pulled in the 5.3 kernel...

https://bugzilla.redhat.com/show_bug.cgi?id=481579

I'm not sure if they'll be back in 5.5, 6.0 or if I'm completely mistaken.

I seem to recall the delay being a result of upstream kernel not accepting the FS-Cache patches (which I believe they did do recently in 2.6.30).

The kernel patches that were in the earlier 5.x kernels are now a bit out-of-date and IMHO not really suitable for production use.

There has recently been a number of new FS-Cache patches/improvements that will be in the 2.6.32 mainline kernel

I doubt FS-Cache will be back in future 5.x kernels - my guess is that it will be in the 6.x kernels

James Pearson

Paul Berger wrote:

I read a CentOS bugzilla http://bugs.centos.org/view.php?id=3853 that indicated that the functionality may exist in the kernels yet, but just the user space tools were missing. After doing some testing, the persistent caching does not appear to be in the kernels, either that or process outlined in the bugzilla entry and http://people.redhat.com/steved/fscache/docs/HOWTO.txt are missing something.

Looks like that CentOS bug listing is not quite right - the FS-Cache code is still in the 5.[34] kernels (and the fscache.ko module is available), but the 'fsc' mount option in the nfs client module has been disabled - from the kernel changelog:

* Sat Sep 13 2008 Don Zickus dzickus@redhat.com [2.6.18-115.el5] ... - [nfs] disable the fsc mount option (Steve Dickson ) [447474]

I also tried the Centos Plus kernel to see if it's be enabled in there and the results appear to be the same.

Apparently I need to use either Fedora 12 if I want to use this feature now, use CentOS 5.2 and not update as waiting till CentOS 6 is not really an option. I really hate using bleeding edge and not updating and running with packages with know security vulnerabilities (even on our internal networkd) seems like a poor idea. ::sigh::

Theoretically, you could rebuild a more recent CentOS 5.[34] kernel with the 'linux-2.6-nfs-disable-the-fsc-mount-option.patch' commented out in the spec file - but as I mentioned previously, the FS-Cache code that is in these kernels is now quite old (and buggy).

If you really need to use FS-Cache now, then you need to use something like Fedora 12 or, as I have recently done, use CentOS 5 with a recent mainline kernel (2.6.32-rc8-git4 has up to date FS-Cache patches) and a more recent nfs-utils version - see:

http://www.redhat.com/archives/linux-cachefs/2009-October/msg00002.html

James Pearson