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Network Storage Help



 
 
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  #21  
Old January 22nd 08, 05:20 PM posted to comp.arch.storage
the wharf rat
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Posts: 34
Default Network Storage Help

In article ,
Faeandar wrote:

I disagree with this. Performance is never better than with local
scsi storage. DAS is still king when it comes to raw performance.


Well, you'd think so, but it's not actually true. For one thing,
you can't really fit eighty or a hundred spindles inside that server case,
and if you find an external enclosure that works you'll need to move to
fibre channel anyway and lose the theoretical speed advantage of a direct
scsi 320 connection. (Maybe if they actually *had* scsi 1280 I'd agree
with you :-) And a SAN is (at least usually) a lot more than just an external
storage cabinet and a fibre strand. These things have multiple raid levels,
even custom raid arrangements, gigabytes of battery backed cache and
sophisticated caching algorithms (one reason throughput to the SAN can be
faster than direct I/O to a local disk. You don't actually hit a disk),
multiple hot spares, redundant controller heads, all kinds of stuff that's
pretty hard to engineer into a standalone server. Couple that level
of architecture with an FC fabric and it's hard to argue that any
kind of point storage is technically superior.

Reliability is actually better in most DAS environments because you
have fewer bits in the middle. No shared cache to get corrupted. No
zoning to go bat**** and lip storm. Things like that.


Hmmmm, well, do you think that an FC fabric is inherently less
reliable than a 40 foot scsi cable? I'm not sure what you mean by shared
cache corruption; the cache in something like an EMC just doesn't somehow
"get corrupted" any more than your server memory somehow "gets corrupted".

  #22  
Old January 22nd 08, 05:51 PM posted to comp.arch.storage
the wharf rat
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Posts: 34
Default Network Storage Help

In article ,
Faeandar wrote:

My experience is that applications that claim they need block access
are incorrect.


That's only trivially true, in that applications don't generally
require block access. What you're supplying block access to is usually
the OS which is in turn interacting with the application via something
like Veritas or OCFS. Certain NFS implementations are approved for use
with Oracle, but there's a performance degradation over a direct access
san device. I don't actually see how you could build a petabyte data
warehouse on top of NFS. IMHO it's just too inefficient.

And Oracle *recommends* using NFS with Oracle RAC, so clustered Oracle
on NAS is preferred.


Do you have a reference for that? I don't remember that as true
as of 10g.


The only things I can think of that *need* _shared_ block level
storage are clustered file systems. Other that that, everything I've
ever run across will work on NAS.


A large mail spool won't. In fact, anything that depends on
reliable file locking will almost certainly break over an NFS link.
I'm aware of the improvements in V4; they still don't support clustered
file systems well.

 




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