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Justifying FS-Cache

Justifying FS-Cache

Posted Dec 25, 2008 15:37 UTC (Thu) by dw (subscriber, #12017)
In reply to: Justifying FS-Cache by dw
Parent article: Justifying FS-Cache

Ignoring that for a second, why can't they just LART their "entertainment industry customers" and have them add 10 lines of code to their app to add caching functionality? This whole thing smells of suck.


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Justifying FS-Cache

Posted Dec 25, 2008 18:56 UTC (Thu) by pkern (subscriber, #32883) [Link]

Well, the obvious thing that they could implement caching here aside. Is there some sane way to speed things like /home on NFS up with a local disk?

Of course one could switch to AFS where the local cache is mandatory, but which might give one weird bugs resulting out of non-POSIX behaviour (e.g. problems with locking). But I somehow fail to see production-ready alternatives for shared home directories. What you usually could get are cluster filesystems on some shared storage device, which are not really suitable for the one server - many clients case, where each client node could be turned off at any time.

Something like FS-Cache could really reduce network traffic and burden for the server here, especially because the clients in my case are equipped with a otherwise mostly unused harddisk. (The root filesystem is currently rsync'ed on them, which still leaves like 100G per client unused.) I would be glad for any other suggestion, though.

Justifying FS-Cache

Posted Dec 26, 2008 13:32 UTC (Fri) by vonbrand (guest, #4458) [Link]

The problem here is precisely the non-POSIX behaviour. The non-POSIXness of NFS is barely bearable, the one of such an "perhaps you get the offline version, perhaps the online one" is madness.

Justifying FS-Cache

Posted Dec 27, 2008 5:54 UTC (Sat) by csamuel (✭ supporter ✭, #2624) [Link]

Well, the obvious thing that they could implement caching here aside. Is there some sane way to speed things like /home on NFS up with a local disk?

NFSv4 already has the concept of file delegations (in fact 4.1 includes read-only directory delegations too), where a client which opens a file that isn't being accessed by other systems can be granted a delegation to operate on that file locally and then either commit the final changes to the server when its done or for the NFS server to recall the delegation if another client requests access.

So if you are running an HPC cluster, for instance, and a user runs a code in their home directory by accident (yes, it does happen, sadly) that uses a lot of temporary files then ideally the server will be able to delegate access to the client and they don't need to do any of their I/O over NFS..

Justifying FS-Cache

Posted Dec 26, 2008 22:56 UTC (Fri) by nix (subscriber, #2304) [Link]

I'm using it to allow my desktop box to boot from NFS, with (almost) no local storage other than FS caching: it's all on a remote system, because that happens to be a five-disk RAID-6 (md) array which I trust my data with more than a single-disk desktop: but I want that desktop to be local-disk fast nearly all the time.

Think of it as a poor man's hierarchical storage.

It rocks. (And it saved my bacon when I had a disk failure half a year ago.) :)


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