Re: [PVFS2-users] pvfs2 possible for high-availibility clusters?

[Jan Lenaerts]

Thanks for your answer

On 11/29/05, Rob Ross <[EMAIL PROTECTED]> wrote:

Hi Jan,

PVFS2 probably isn't what you're looking for, but I'll try to help
anyway :).

why is PVFS2  not what I'm looking  for? As far as I understand it is possible with PVFS2 but not optimal in case of serial and small-file workloads. What would be better for database and an apache server?

PVFS2 (along with GFS, GPFS, Lustre, others) will do all the things that
you describe in a single package (slightly reworded):
- present lots of disks as one logical space
- provide access to that logical space from many clients/nodes
- coordinate access to provide consistency during concurrent access

So you don't need to worry about using one thing to organize the disks,
another thing to get the access to them, and a final thing to create the
file system.  iSCSI and/or FC may come up when fault tolerance comes
into play, as described next.

PVFS2 will also run in a fault tolerant configuration, but to do that
multiple servers need access to the same storage.  Usually that requires
purchasing some FC or iSCSI hardware and dual-attaching to a couple of
nodes.  Most cluster file systems make this requirement for fault
tolerance.  Software redundancy (with performance) in this environment
is very hard, and as far as I know no one is giving away an implementation.

you lost me here, I thought the multible servers already had access to the same storage (the shared PVFS2 filesystem) via the network card.
why would I need iSCSI hardware can't I simulate it with something like http://sourceforge.net/projects/iscsitarget/
it is still not clear to me how PVFS2 is fault tolerant? I thought the filesystem stays available but the data on the failed node is unavailable? or is the data also mirrord on an other node?
 

greez,
Jan

PVFS2 is different from most cluster file systems in that we don't do
client-side caching or locking.  This is good for fault tolerance
because it simplifies failover scenarios, but it is bad for serial and
small-file workloads because operations always go over the wire, and
that can be slow.

Hope that helps,

Rob

Jan Lenaerts wrote:
> hellow,
>
> The past hour I've been reading about PVFS2, but it's still not clear to
> me, if PVFS2 can do what I want or not.
> Let me explain:
>
> I have 4 node's in a high availibility cluster, I want to bundle a part
> of diskspace from each node, and use that as a shared filesystem for my
> nodes.
> so I need:
>
>     * something that can bundle the diskspace(PVFS2 maybe? )
>     * something to share the disk to each node(iSCSI target &
>       iSCSI_initiator)
>     * a FS that won't get corrupt when multible nodes read or write on
>       it(GFS or OCFS2)
>
> - But PVFS2 is already a filesystem is it possible to format GFS on top
> of that?
> - PVFS2 is at filesystem level, is it possible to share it on
> block_device level to each node, as with iSCSI?
> - does it preform good as FS for apache, mysql etc... ?
> - If one node (dataserver fails) is the data somewhere else available? I
> guess the data on that node is then unavailable? witch is unacceptable
> in my case. Is there a way to do this?
> - if PVFS2 isn't what I need, Then what is out there to become complete
> fault redundant storage, something like
> http://www.capricorn-tech.com/products.html or what I want
> - How can I achieve this, is there maybe a guide that explains a setup
> like I would like?
>
> Thanks in advance,
> Jan Lenaerts

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