Both.
Degradation is inherent to the concept of shared storage. Either you trust the
fact that you're alone on a disk and use diskcaching or you're not and you need
to use some other mechanism to sync the changes amongst the participants. This
can be via I/O or via the network, so you always have delay and bandwith usage.
So, if you would compare ext3 on san disk to a gfs or clvm volume, you would
get a performance hit. But, would you say, those are things you can't compare
as gfs en clvm does things an ext3 on a san disk can't. True. But do we _need_
those things ? No. In fact, we do _not_want_ the ability to start the same domu
several times on different machines. And by letting the domu use the san disk
as a dedicated disk, it can use its diskcache without taking any other machines
in to account. Even live migration is not a problem, as the memory ( and thus
the disk cache ) just get migrated too ...
I simply do not see the added value of using a clustered filesystem for a domu.
And in that light, any additional overhead is too much. Why make things complex
? Complex setups have complex problems in my experience. We solved the problem
with a very simple script, checking all cluster members to see if a specific
domu was running or not. Does this weigh up to having to learn,administer,tune
en possibly debug a clustered file system ?
Lastly, I really don't see the $/GB argument. A GB cost the same, although its
a bit slower on a clustered filesystem, that's all.
Peter.
Ps: nice line-up of acronyms, btw 8-)
On Monday 08 September 2008 17:30:25 Javier Guerra wrote:
> On Mon, Sep 8, 2008 at 10:23 AM, Peter Van Biesen
> <peter.vanbiesen@xxxxxxx> wrote:
> > We tested that too. It is overkill and degrades performance.
>
> do you mean GFS/OCFS, or CLVM/EVMS?
>
> the former have obviously higher overhead, the later shouldn't....
>
> it's important because if you don't have netapp-level storage
> subsystems with great administration, then you can do iSCSI/AoE/gnbd
> and CLVM, and get great $/GB results with still really good
> administrability.
>
--
Peter Van Biesen
Sysadmin VAPH
tel: +32 (0) 2 225 85 70
fax: +32 (0) 2 225 85 88
e-mail: peter.vanbiesen@xxxxxxx
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