[Linux-cachefs] Fedora kernel testing

[Daire Byrne]

David,

----- "Daire Byrne" <Daire.Byrne at framestore.com> wrote:

> I have been testing a "live" Linux USB stick distro that we intend to
> give to employees who are working from home (VPN). They put the USB stick
> in their Windows or Mac PCs and it boots up an environment identical to the
> Linux setup in the office. All our NFS (automount) maps are accessible and
> fscache stores data on the USB stick. In tests this has been working great and
> is a very useful way of teleworking.

After testing this over the last couple of weeks I am quite happy with 
the results - NFS caching is great for VPNs and teleworking! There are 
a few things that still could be better though.

Does it make any sense to have a concept of "lazy" netfs lookups whereby
if I know that the netfs filesystem won't be changed I can go straight to
the cache and not have to go to the network at all? Maybe not quite 
disconnected in the sense that perhaps you can relookup the network every
10 mins or so. This would be great for high latency networks and small file
access. Also would it be possible to cache the contents of dir in a similar 
fashion? So for example if I mount my home dir over a slow link and have 
some subdir in my PATHs, applications will only need to go to the network
the first time to check the existence of a file in a dir (e.g. PATH etc.).
With something like Lustre perhaps this all becomes far more efficient due 
to the DLM - you only go to the network when you are notified of a PAGE
change? Or would you need to keep locks on all cached files for that?

Another application for NFS caching I was thinking about was for storing VM
images. It is necessary to keep VM images on shared storage for easy 
migration but you want to minimise the NFS traffic and utilise local storage
if possible. Would caching the read parts of the image on disk should help? 
Like before if I know that the VM instance is based on a read-only QCOW2 image
would it help to force the NFS cache to never revalidate what is on the net
and go straight to the cache? Obviously writes always have to go to the net.

Apologies if these questions are a bit silly - I'm not much of a programmer!

Daire