DAS isn’t a curse word

I deal with this from time to time where users (and admins too unfortunately) will not only shy away from DAS, but actually act like it’s some kind of computer virus.  Now that SAN is here and is so ubiquitous nobody thinks DAS is worth anything anymore.  I’m fully aware of all the arguments, but remember DAS gave us some really nice control over our disk layouts and we didn’t have to keep going to the SAN guys to ask them for dedicated spindles, which is something they hate to give.  And that’s really something to be said for a DAS isn’t it?  We don’t have to worry about our DAS spindles being shared with 10 other servers. 

So whenever someone talks about DAS vs SAN, I always try to insert some reason into the debate.  SAN is good for what it’s good at, but so is DAS.  And there are often times I miss the DAS days.  I never had to fight with a SAN guy about whether the SAN can handle all of the disks being on the same physical partition.  I never had to try to explain to them that a DB isn’t a file system and you can’t just put everything on the same chunk of disks with 10 other servers.  I never had to get special permission to have a different RAID level put on the server.  But don’t get me wrong, I’m not anti SAN.  I just don’t think people give DAS its due credit anymore.  For a lot of systems in your shop, a couple DAS cabinets on each server can ease some of your I/O trouble.  And of course, that’s at the cost of management for the disk guys, but everything comes at a cost.

3 thoughts on “DAS isn’t a curse word”

  1. For what it’s worth, we got a SQL 2005 instance running on an active/passive solution with DAS, configured in RAID 10 across the board. I have no complaints about its performance.

  2. Still remember looking at a box that was IO bound. We were moving to a SAN solution and all I heard was “we’re giving you all of this space”. I kept telling them that “all this space” wasn’t the problem. We needed “all of these spindles” to solve the issue. Had IO numbers, graphs, all sorts of proof, but they kept thinking “space == IO”. Never did find out the outcome of that battle as I’d moved on before it was ever resolved, but it was a really hard fight.

    We had a DAS solution in place at the time that lasted us right to the point in time we had originally planned and could easily have gone longer without too much trouble. There’s a lot to be said for DAS. Sometimes it’s just a solution that fits well.

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