We have an EMC San - CX4-240C filled with 15k (4Gb) Fibre Channel disks setup in RAID 5. Our applications that run on this SAN do primarily Sequential read and write of large text data files. I'm testing throughput and seeing a high water mark around 125 MB/sec when nothing else is running on the server. That seems slow...
In contrast, we have another server attached to a Dell MD1200 SAS based system filled with 15k drives as well. We have a RAID 10 on that configuration and get about 485 MB/sec of performance.
Is a DAS based device always going to smoke a fibre channel SAN for this type of performance comparison? Doesn't 125 MB/sec seem slow for pure sequential access on this type of SAN? I know there are a number of other considerations, but looking for some general feedback.
Answer
Are other devices using that spindle, or shelf, or FC link to the SAN from the switch?
Your test isn't necessarily happening in isolation on the SAN, whereas it likely is with the DAS. Combine that with the fact that the disks in the DAS are probably newer and faster than those in a CX4, and that RAID 10 is faster than RAID 5, and there's certainly enough other variables that placing the blame on the fact that the SAN is a SAN isn't terribly appropriate.
So, to more directly answer your question: no; a SAN is not inherently slower than a DAS in any way.
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