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Re: Was: iostat output; Now: Disk storage technologies

From: Matthew Zito <>
Date: Thu, 29 Apr 2004 20:34:38 -0400
Message-Id: <>

I'm not cringing at all - quite the contrary. DBAs are hampered today by the fact that their applications, moreso than most others, are closely tied to the storage the servers are attached to. At the same time, though, storage technology has become complex enough that its practicaly a whole separate skill set. So, Oracle DBAs ideally have to be experts at both - a tall task, to say the least.

Storage vendors haven't helped this either - they've found a lucrative market in professional services for their storage products and are invested in the "CIO sell". When I was at EMC, I took their sales training, and the conventional wisdom was that it was a waste of time to sell to DBAs and other "pure tech" customers- to ignore them and go right over their heads to their management.

DBAs are thus kind of left out in the cold - ignored by the vendors, pushed towards consultant implementations, poor documentation, and a constantly developing set of technologies. It's a rough road.

To go on to the pure tech topics, I think the biggest correction I would make is that SAN == high end. This certainly was true 5-7 years ago, but today, SAN is available to every organization. EMC, HP, and Dell are all working on shipping a SAN bundle for sub-$10k prices. The end result of this is that DAS is going to be pushed out of existence - its only a matter of time. Now, its true, the low-end SAN products don't ship with the featureset of the large monolithic arrays (HP XP-series, EMC Symmetrix, HDS 9980), but they are effectively supplanting DAS in new installs.

The performance and featureset of NAS is a common misconception as well. I'm definitely a NAS cheerleader, within reason, but NAS has rapidly moved out of the realm of office fileservers and development environments into serious large-scale and high-performance environments. BlueArc, for example, ships a NAS array capable of over a 1GB/sec. of I/O, and they're going to be up to 2GB/sec. by the end of the year. In addition, the higher-end NAS boxes from companies such as Network Appliance and BlueArc support all of the features you tied to SAN - dial-home, dynamic cache partitioning, snapshots, remote replication, etc.

It gets even MORE complicated when you look at the multi-protocol support available on some of the arrays. NetApp filers support NAS, Fibre Channel, and iSCSI all from the same box (and exposing the same storage through multiple protocols!) - EMC Symmetrix does both iSCSI and FC from one array.

Which dovetails nicely into iSCSI - iSCSI will replace Fibre Channel at some point. Fibre Channel is just too expensive (still around $1000/port!) and complex to last in the face of iSCSI, which can run over existing networks, leverage already-developed skillsets and provide identical performance. The only limiting factor for iSCSI today is the relative newness of the implementations and the lack of good hardware offload cards. The reason fibre channel is so fast is because most of the protocol is handled in dedicated processors on the card, leaving the host free to do other things. Software iSCSI over normal gigabit cards has to do all of the I/O on the host CPUs, significantly decreasing the throughput. At the moment, iSCSI is neither a low-end or high-end solution - its more of a solution for early adopters looking for block-based I/O at a lower price point.

Hopefully this is informative - thanks for the chance to pontificate...


Matthew Zito
GridApp Systems
Cell: 646-220-3551
Phone: 212-358-8211 x 359

On Apr 29, 2004, at 1:05 PM, John Kanagaraj wrote:

> Matt,
>> You can respond to me directly if you like - unless the list at large
>> is interested in iSCSI on netapp.
> I would very much like to keep this in the list..... The ground
> beneath us
> as far as storage is concerned is moving quite quickly, and most of us
> DBAs
> are still in the dark as far as Storage concepts and directions go.
> Many are
> not aware that there is a wide variety of solutions as far as disk
> storage
> is concerned, and the DBA world is just now getting a handle on the
> transition from DAS (Direct Attached Storage) to SAN (Storage Area
> Networks)
> or NAS (Network Attached Storage). And in comes comes iSCSI (or a
> combination of the above) to cloud the picture.... As far as I
> understand
> the technology, we have:
> -----------------------------------------------------------------
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Received on Thu Apr 29 2004 - 19:31:17 CDT

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