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Mixing SAS and SATA drives on a new SAS backplane

Posted on 2014-09-22
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Last Modified: 2014-09-26
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. Is that really true?

 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). I have the drives.

 Option 1- Connect drives as planned to the backplane. Why should they not be mixed if raid controller allows both? I am not extending the backplane and there is no logic done there to my little knowledge, so I don't understand the warning from Supermicro about not mixing drives on the backplane. The Intel SSDs are enterprise level drives, the best I could afford, and I'm not aware of any better.

 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
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Question by:Daniel Watrous
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by:andyalder
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It is odd that the manual says not to mix SAS and SATA in the same enclosure, the datasheet for the MG9072 chip that handles enclosure management says it supports both.
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by:Daniel Watrous
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Hi andyalder,

Supermicro SAS743TQ pdf manual
http://www.supermicro.com/manuals/other/BPN-SAS-743TQ.pdf
#10. - #17. SAS Ports The SAS ports are used to connect the SAS drive cables. The 8 ports are designated #0 - #7. Each port is also compatible with SATA drives. However, do NOT mix SAS and SATA drives in the same enclosure.     page2-3

Should have included this from the manual, which I wish I hadn't read, as my web research hasn't found any problem with mixing other than using cheap SATA disks on a business server to save money and crying later about data loss.

dan
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Brian Hewes earned 500 total points
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You might be able to mix and/or match different interfaces. But, you should follow the manufacturer instructions. By attempting to do anything different you might void one or more active warranties.

Also, you may see a degrade in performance due to a controller being confused, or automatically downgrading the overall performance to match the performance of the slowest partner in the enclosure.

It's just not worth it.

Blessings!
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by:Daniel Watrous
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Thank you Brian,

I take that to mean that you are recommending Option 4, which is to switch my SAS 4TB drives to SATA 4TB enterprise drives. How would you rate the relative risk between data loss from using SATA drives instead of SAS drives vs. confusing the controller with both types of drives? How much risk is there from switching to SATA enterprise drives?

Dan
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by:andyalder
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Unsolved as to why SuperMicro impose the limitation whilst the RAID card manufacturer and the SES chip manufacturer impose no such restriction. Maybe they're just covering their arseholes.
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