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Mixing SAS/SATA on Backplane

Tags:
  • SAS
  • NAS / RAID
  • SATA
Last response: in Business Computing
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September 21, 2014 2:58:35 PM

Hi,

I need some advice to pick the best option.

I bought a barebones supermicro server with a LSI megaraid 9361-8i raid controller with write back cache, which tolerates SAS or SATA drives. It has 2 mini SAS ports internally that are connected with mini SAS 1 to 4 cables to the backplane (Supermicro SAS743TQ for an 8 drive enclosure), but the backplane's documentation states all drives should be either SAS or SATA.

My plan was to have 3 SATA intel s3700 SSDs (raid 1 with hot spare for OS and applications) with 5 SAS WD 4TB HDDs (raid 10 with hot spare for archival data). Yes, I have the drives.

Option 1- Connect drives as planned to the backplane. Why should they not be mixed if raid controller allows both?

Option 2- Use a mini SAS 1 to 4 SATA adapter to connect the raid controller to the SSDs, bypassing the backplane for the SSD drives. I would have to take the hot spare away from the archival data array, not a big loss, as I would be limited to 4 SAS drives. My problem is putting the SSDs securely in the LFF enclosure as the 3.5" to 2.5" adapter is meant to position it properly for the backplane. Is there a universal adapter that holds a sff drive away from the backplane? Thought I'd ask here before trying with supermicro.

Option 3- Use software raid for my SSDs and the expensive LSI controller just for the SAS drives. My motherboard has 10 SATA ports, 2 peach and 8 white (not sure what that means). Anyway, same problem as in Option 2 that I won't be able to use the spiffy 3.5" to 2.5" drive adapters since they push the drive onto the backplane, so either a different adapter or the SSDs don't go in the drive enclosure and I don't get the little lights to watch for functioning drives.

Option 4- Replace the SAS 4 TB HDDs with SATA 4 TB HDDs. What I get for buying them already, but I have always used SAS drives in servers.

Option 5- Something you would recommend other than the above.

Appreciate your advice. Seems there a lot of people mixing SSDs and HDDs, so I'm hoping mixing SAS and SATA on a backplane is a known issue.

Thanks,
Dan

More about : mixing sas sata backplane

Best solution

September 23, 2014 11:47:09 AM

My simple thoughts:

If SAS is really important to you, you may want to check for a firmware update that might allow mix & match SAS/SATA connections. I believe with some of Dell's PERC controllers (based on MegaRaid), they allow for that type of scenario. So likely you can get an update for your LSI MegaRaid controller.

However, I would go to a SATA-only setup with that controller as a price & performance upgrade. A SATA SSD array will easily out-perform a SAS array of spinning disks (HDDs). You can create two arrays of SATA drives - 1 array of SSD (I would go for a 3 x SSD +1 hot spare RAID-5 or add another SSD for a RAID-6) as your high-performance storage, and 1 array of 4TB SATA (go with the enterprise class of HDDs) for your lower-performance archival storage array.

If you're rolling your own array, you may not have to go with the higher-cost Intel S3700 drives. I would recommend looking at the Samsung 845DC PRO (great write endurance!) or the Micron 500DC as a lower-cost but still high-performing alternative to the S3700. If absolution write performance isn't as high of a priority (for example, if this is for a webserver which is most read-only), then you can go with the SSDs that target read performance, like the Intel S3500, for a much lower cost.

As a final note, I also recommend buy an extra drive of each type when you roll your own arrays. That way, if one goes out, you will have a backup right there to plug in immediately, rather than trying to source the same drive later on.
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