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6 GBit backplane + 3Gbit Disk = ?

B

brutalizer

[H]ard|Gawd
Joined
Oct 23, 2010
Messages
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If I use 3GBit disks, what will happen when I combine it with 6Gbit backplanes, and LSI cards? Will everything run at 3Gbit? Or will I get 6Gbit in total, because each disk uses 3Gbit out at the end of the chain, but the rest of the chain (backplane, LSI card) use 6Gbit?

Or will any 3Gbit component drag everything down to 3Gbit?

In other words, is it important to use 6Gbit disks to reach full speed? Or can I mix 3Gbit disks and 6Gbit disks?
 
The SATA II disk will run at SATA-II speed max and the SATA-III disk will run at SATA-III speed max or at least that is what my LSI cards at work say. For hard disks this does not make any difference since there does not exist a hard drive that needs SATA-III speeds.
 
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At work on an LSI 9201-16i I have 10 Seagate 7200.11s and 2 hitachi 7k3000s connected to 3 supermicro 5 in 3s. The LSI card shows that the 2 SATA-III drives are communicating at SATA-III speeds while all others are using SATA-II. I have been testing this for a few weeks creating and destroying raid6 arrays and copying data to and from the 2 7k3000s in raid 1.
 
Here we have some additional information:
http://hardforum.com/archive/index.php/t-1579928.html
And you should not use 3GBit disks in this case? Is it because the LSI SAS expanders do not implement "SAS multiplexing"? What is SAS multiplexing?


"Back to the SuperMicro chassis...my only real disappointment with this case is the LSI SAS expanders used do NOT implement SAS multiplexing...this means if you populate the case with 3Gbps drives (e.g. Sata) your uplinks (SAS connections between the HBA and enclosure) WILL negoitiate to 6Gbps, however, ever other "frame?" will be a "pad" frame so you will only realize 3Gbps of throughput per channel on the uplinks.

This is not a huge deal as you can still achieve 2000MB/s through this chassis...perhaps even more if you use SAS multilink--that is connect TWO SAS wide ports to each of the 2 SAS expanders in this chassis (remember there is a SAS expander for the front drives and a second expander for the rear drives)....I haven't tested this yet, but from what odditory has reported that should give you even more boost.

If you REALLY need this chassis to perform at it's true capability you need to populate it with SAS 6Gbps drives..."
 
Expanders are a different matter. I can not answer for those since I do everything I can to avoid their usage.
 
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