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I'm setting up a server that will need to be accessible 24/7 but will be rarely accessed (archive storage). To save heat/power, I'm thinking of setting hard disks to spin down using hdparm.

However, I wondered if this could cause unreliability as the storage is a Linux RAID 10 array. i.e. could delay in spinning up cause a drive to be kicked out of the array. Any experiences/war stories on this?

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3 Answers 3

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I've done this with a Linux raid-5 array, and never had any trouble from it sync-wise. There was a noticeable lag when the drives would spin up, about 45 seconds or so. Power-wise, though, I've decided it wasn't really worth it. The server consumed 90 watts when the drives were spinning (it was build with power consumption in mind), and 70 when they were spun down. That difference didn't justify the wait time from spinning them back up.

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I've done this before (5+ years ago) and never saw any problems with spinning down the disks. Unless the disk doesn't spin back up, it should be ok. Your access times will suffer though. Pick a good spin-down time - something that will keep the disks spun up during the time you'll use them. I chose 15 minutes. It was generally good during use, and when I stopped using the disks (overnight for example) it spun down soon enough.

I don't know what kind of power savings you'll get - I spun down disks to cut down on noise. I wasn't using the best disks...

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Thanks for your answer. Agree with you on power side. I'm also spinning down to control heat and noise. –  bugmenot77 Mar 10 '10 at 18:52

Consider not using Linux (raid). Get an Adaptec SAS card.... which allows you to do a lot more than what you intend.

Anyhow, it can:

  • Handle automatic failover to a reserve disc
  • Handle regular spin ups to make sure the discs work
  • Handle regular validation of the complete RAID

All that keeps the items running properly. Plus you can scale to around 190 discs in cascaded SAS enclosures should the need arise ;)

Consider using RAID 6, not RAID 10 - gives you better performance for more discs than 4, and... well, if that is an archive, anything else is not really needed. Raid 10 is more for high end database servers.

Depending on the size of the RAID, spin up may be problematic during the day. You may not be properly able to spin up all discs at the same time.... and if you stagger the spin ups (can Linux do that?) it may take longer to acutally get them all operational than users may like. Under this case it may be advisable to keep the discs spinning during the day. If that is a new server, for power saving, consider 2.5" discs. Supermicro has a nice cace tha tis 1 rack units and has space for 24 hard discs 2.5" - and a lot more for 3.5", up o 48 or so in one case.

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First - this isn't an answer to the question. Second - RAID 6 will almost never outperform RAID 10. Third - You didn't list a specific card and there are dozens of Adaptec SAS cards. Every feature of the mystery SAS card that you mentioned is something that the OP didn't ask about or doesn't apply to the question. –  MDMarra Mar 9 '10 at 20:59
    
First, it is - it is a war story for a storage system. Second, there are not dozen, there is one current LINE of different cards based on port requirements, mostly. Gratulations, you successfully managed to be an ass. –  TomTom Mar 9 '10 at 21:11
    
I'd like to see numbers that show that RAID 6 is higher performance than 10. and second - according to this adaptec.com/en-US/products/Controllers/Hardware it sure seems that there are over a dozen SAS cards from Adaptec with very different feature sets –  MDMarra Mar 9 '10 at 21:16
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Linux software RAID is awesome when there's not justification for the additional cost of a hardware RAID. While RAID6 won't give better performance than RAID1+0, it might be a more efficient use of resources for an archive server. –  Warner Mar 9 '10 at 21:54
    
@Warner - You definitely get more bang for your buck space-wise with a RAID 5 or 6, no doubt about that. My comment was because TomTom specifically says RAID 6 will outperform RAID 10 at a spindle count higher than 4. –  MDMarra Mar 9 '10 at 22:14

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