Re: Postgres over Linux NBD or NFS

There are some less expensive baby-SAN options coming out now - Dell
has an
rebranded EMC baby SAN (which of course doesn't work with any other EMC
system...) that starts at about $6000 or so. Just read the announcement
- don't know
anything else. While there have been some reports of undewhelming
performance for
database applications, the Apple XRaid has a sweet price point,
particularly if you're
in an industry that they want some exposure in (we're in financial
services, they almost
gave it to us...$7000 for 2TB, batteries, accessory kits, etc), and a
decent feature
set. It works with non-Apple stuff..

The baby-SANs don't necessarily do many of the things that you can get
out of a full-blown
EMC/NetApp rig, but then again, you're not paying for it either.

There are a lot of lower-cost storage options popping up now, as
IDE/SATA disks arrays
proliferate. You can get external RAID boxes that talk SCSI or fiber
with IDE disks for
dirt these days. Small, too. Portable. I'm see little need to buy
massive boxes with
internal storage arrays anymore.


On Jun 22, 2004, at 7:50 AM, Christopher Browne wrote:

> In an attempt to throw the authorities off his trail,
> ronz@ravensfield.com (Andrew Rawnsley) transmitted:
>> On Jun 21, 2004, at 2:02 PM, Andrew Hammond wrote:
>>> We're looking for an alternative to fiber-channel disk arrays for
>>> mass
>>> storage. One of the ideas that we're exploring would involve having
>>> the
>>> cluster on an NFS mounted filesystem. Another technology we're
>>> looking
>>> at is the Linux NBD (Network Block Device).
>>
>> No idea about NBDs, but its generally accepted that running over NFS
>> would significantly decrease reliability and performance, i.e. it
>> would be a Bad Move (tm). Not sure what you think to gain. I sure
>> wouldn't trust NFS with a production database.
>>
>> What exactly are you trying to gain, avoid, or do?
>
> The point of the exercise is to try to come up with something that is
> a near-substitute for a SAN.
>
> With a SAN, you have a box with a whole lot of disk in it, and then
> your database servers connect to that box, typically via something
> like fibrechannel.
>
> One of the goals is for this to allow trying out Opterons at low risk.
> Should performance turn out to suck or there be some other
> disqualification, it's simple to hook the disk up to something else
> instead.
>
> The other goal is to be able to stick LOTS of disk into one box, and
> dole it out to multiple servers.  It's more expensive to set up and
> manage 3 RAID arrays than it is to set up and manage just 1, because
> you have to manage 3 sets of disk hardware rather than 1.
>
> But I'm getting convinced that the attempt to get this clever about it
> is counterproductive unless you have outrageous amounts of money to
> throw at it.
>
> - NFS may well be acceptable if you buy into something with potent FS
>   semantics, as with NetApp boxes.  But they're REALLY expensive.
>
> - FibreChannel offers interesting options in conjunction with a fairly
>   smart SAN box and Veritas, where you could have 5TB of storage in
>   one box, and then assign 2TB apiece to two servers, and the other
>   1TB to a third.  But the pricing premium again leaps out at ya.
>
> The "poor man's approach" involves trying to fake this by building a
> "disk box" running Linux that exports the storage either as a
> filesystem (using NFS) or as disk blocks (NBD).  NFS clearly doesn't
> provide the filesystem semantics needed to get decent reliability;
> with NBD, it's not clear what happens :-(.
>
> Barring that, it means building a separate RAID array for each server,
> and living with the limitation that a full set of disk hardware has to
> be devoted to each DB server.
> --
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> http://www3.sympatico.ca/cbbrowne/
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Andrew Rawnsley
President
The Ravensfield Digital Resource Group, Ltd.
(740) 587-0114
www.ravensfield.com