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Does it make sense to have 15k HDDs / fast raid configurations in a server connected to Gigabit Ethernet. Surely the HDDs would only become the bottleneck when you get into the realms of Fiberchannel SANs?

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closed as not a real question by Chris S, gWaldo, Massimo, Ward, mailq Nov 1 '11 at 17:53

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You can't possibly make an argument related to disk speed without any context based solely on the network connection speed. If all the server does is shuffle data between the network and disk, then yes, this might be meaningful. Otherwise an app server might do 1000x as much disk IO as NIC IO. –  Chris S Nov 1 '11 at 17:01
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3 Answers

You can't equate network performance and disk performance without telling us the application. If your disks are housing a database with an 80% random read workload of small block IO, then the network will almost never be the limiting factor, the seek time (and IO/s) of the disk array will be.

If you're streaming video or doing CIFS/NFS file sharing, then you are more likely to see your network be the bottleneck.

Also, little known fact: SAN performance is usually designed to try and equal the performance per head of locally attached drives, not surpass it. Local drives have the advantage of an internal data bus, and the only time centralized external storage will beat local drives in performance is when they are using their larger cache, applying more spindles to a job than would be feasible in a direct attach environment, or using SSD.

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+1. I have a 8 x 10k Raptor Raid 10 here and I sometimes get only a low double digit Mbyte (10, 12) when the IO is small and totally random. –  TomTom Nov 1 '11 at 17:45
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If disk access is not your bottleneck, then no. But faster disks make for faster disk reads.

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Of course they are. I can't stand long wait times when firing up Starcraft II or Battlefield [insert appropriate version number here].

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