[Linux-cluster] Does GFS work well with hybrid storage devices?

[Jonathan E Brassow]

On Nov 3, 2006, at 3:48 PM, Lin Shen (lshen) wrote:

> Will GFS work well in a cluster system that hosts a wide range of
> storage
> devices such as disk array, hard disk, flash and USB devices? Since
> these
> devices have very different performance and reliability behaviors, it
> could be
> a challenge for any CFS, right?

Firstly, a cluster file system needs all nodes in the cluster to be 
able to see the storage if they are to mount the file system.  So, 
flash and USB devices are not really suited to a cluster filesystem.

You can have storage devices that are viewable by all cluster nodes and 
have vastly different characteristics (GNBD/iSCSI storage, FC disks, 
arrays, etc).  GFS will work, but it doesn't mean it's good for 
performance.  Taking it to the extreme, I could take a USB device, 
export it to all cluster nodes using GNBD and merge that with some fast 
array.  I could then put GFS on that, but what kind of sense would that 
make?

> I read from somewhere that GFS doesn't support multiple writers on the
> same file
> simutaneously. Is this true?
>

That's probably a mischaracterization of what GFS does.  GFS does not 
allow multiple machines to update the metadata on the same file at the 
same time.  It does allow multiple writers to the same file at the same 
time.  This is no different than a single machine with two processes 
writing to the same file at the same time... you can't be sure of the 
contents of the file (unless you are doing application level locking), 
but you can be sure your file system won't be corrupted.

  brassow