A SAN Primer

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A SAN Primer

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DCPeterson SSCoach Points: 15266 More actions · Answer 1

In terms of performance, also keep in mind that not all SAN's are created equal. A former employer switched from one brand to another (Xiotech to EMC) and immediately we noticed a 20% - 25% improvement in out IO throughput. The increase was large enough to be very noticable to our users.

Of course the improvement was anything but free. Both there and at my current employer we calculate the cost of the EMC storage to be $220 per GB! Certainly not cheap. But in a little more than six years combined usage neither company has ever experienced data loss due to system failure. That, in my opinion, is the real reason to use a good SAN.

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If most people are not willing to see the difficulty, this is mainly because, consciously or unconsciously, they assume that it will be they who will settle these questions for the others, and because they are convinced of their own capacity to do this. -Friedrich August von Hayek

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DCPeterson SSCoach Points: 15266 More actions · Answer 2

In terms of performance, also keep in mind that not all SAN's are created equal. A former employer switched from one brand to another (Xiotech to EMC) and immediately we noticed a 20% - 25% improvement in out IO throughput. The increase was large enough to be very noticable to our users.

Of course the improvement was anything but free. Both there and at my current employer we calculate the cost of the EMC storage to be $220 per GB! Certainly not cheap. But in a little more than six years combined usage neither company has ever experienced data loss due to system failure. That, in my opinion, is the real reason to use a good SAN.

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If most people are not willing to see the difficulty, this is mainly because, consciously or unconsciously, they assume that it will be they who will settle these questions for the others, and because they are convinced of their own capacity to do this. -Friedrich August von Hayek

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Hugh Scott SSC Eights! Points: 987 More actions · Answer 3

Many thanks to all for your posts. Some thoughts to add (in no particular order):

I have written an additional article based on my experiences designing storage on our array. It is currently being edited and will be published in the future on this site.

I did not mean to confuse NAS with SAN, but I am not certain that I did either. I tried to highlight that the newer (since late 2004) CX series from Dell/EMC feature iSCSI which allows users to share ethernet and storage traffic on the same network. I don't believe that these would be considered NASs.

I do not have a great deal of experience with different SAN vendors. I did not highlight the brands I currently use in the article because it wasn't a product review and I did not want it to appear as such. That said, we have installed here a Dell/EMC CX400 (all Fibre), a Dell/EMC CX500 (all Fibre) and an IBM DS4300 (all fibre). We use McData switches with the Dell equipment and Brocade switches with the IBM. All told, I think we have around 12 TB of raw storage. In a previous job, I was privileged to use a Symmetrix SAN (EMC) with their TimeFinder SQL Integration Module (TSIM). What a pleasure to "snap" an 80 GB full database backup in 3 seconds!

With respect to DAS, I have previous experience with an IBM SCSI (can't remember the model) and current experience (not altogether pleasant) with the Dell PowerVault 220S (1 configured in a cluster, 1 configured as a split bus). It's not fair for me to compare the performance with our SAN because the DAS is in our test environment and we have made some deliberate compromises in order to save $$$.

As regards performance, I could not be more pleased with the Dell/EMC line. Two nights ago we loaded a copy of a 279 GB Oracle database from a FireWire External Drive (Maxtor OneTouch II). The copy process took about 68 minutes (and I had to remove one of the HBA's to fit the PCI FireWire card, so there was no load-balancing during the copy process). I regularly back up a 200 GB database in about 45 minutes on a different production SQL Server.

Regards,

Hugh Scott

jlv1 SSC-Addicted Points: 425 More actions · Answer 4

jlv1

SSC-Addicted

Points: 425

June 24, 2005 at 6:33 am

#568249

Great article!

Thanks

CGSJohnson SSCertifiable Points: 7208 More actions · Answer 5

How often are you doing SAN snapshots (both full database and transaction log snapshots, right?) and how often are you backing up to tape, after the SAN snapshots occur? Thanks.

Chris