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post #11 of 16
Quote:
Originally Posted by redsox83381 View Post

Thank you. So what you're saying is that 10 SAS Drives connected through that one SAS cable can all theoretically transfer at 6Gb/s simultaneously? (Assume the drives are capable of that speed).

No..... that single SAS port can only do 6Gb/s max (less due to overhead) regardless of how many drives on the expander.

See image with SAS 12Gb/s:
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post #12 of 16
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Quote:
Originally Posted by DuckieHo View Post

No..... that single SAS port can only do 6Gb/s max (less due to overhead) regardless of how many drives on the expander.

See image with SAS 12Gb/s:

Ok, so if I connect a front end server to a back end JBOB with one SFF 8088, the most data that could be transferred between two is 6Gb/s (750mB/s)? Can I use two to combine bandwidth?
    
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post #13 of 16
Quote:
Originally Posted by redsox83381 View Post

Ok, so if I connect a front end server to a back end JBOB with one SFF 8088, the most data that could be transferred between two is 6Gb/s (750mB/s)? Can I use two to combine bandwidth?

I dont believe you can "trunk" SAS ports - would be interesting to explore but not currently.

To clarify what I was trying to say also is every single port in a "6Gb/s" system will transfer at max 6Gb/s. The diagram posted above explains this pretty well actually. Sorry if I wasnt clear before. To be honest though, if these drives you are using are not SSDs, it will take quite a few to actually saturate that bandwidth.

What are you using this for? You mentioned that you have 10 drives, but what kind of drives? I dont have a link off the top of my head but I remember reading that most drives will average around 150 Mb/s sustained reads. I am assuming youre not just doing purely sequential reads off these are you?
post #14 of 16
Thread Starter 
Quote:
Originally Posted by Ximius View Post

I dont believe you can "trunk" SAS ports - would be interesting to explore but not currently.

To clarify what I was trying to say also is every single port in a "6Gb/s" system will transfer at max 6Gb/s. The diagram posted above explains this pretty well actually. Sorry if I wasnt clear before. To be honest though, if these drives you are using are not SSDs, it will take quite a few to actually saturate that bandwidth.

What are you using this for? You mentioned that you have 10 drives, but what kind of drives? I dont have a link off the top of my head but I remember reading that most drives will average around 150 Mb/s sustained reads. I am assuming youre not just doing purely sequential reads off these are you?

I'm going to have 44 disks in a JBOD. 1 SAS cable per expander so 22 drives per SAS cable. Assuming 100MB/s sequential read speed, that's 2,200MB/s sequential reads.

No it won't be purely sequential reads but there will be some.
    
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post #15 of 16
Quote:
Originally Posted by redsox83381 View Post

I'm going to have 44 disks in a JBOD. 1 SAS cable per expander so 22 drives per SAS cable. Assuming 100MB/s sequential read speed, that's 2,200MB/s sequential reads.

No it won't be purely sequential reads but there will be some.

In that case what most people I know of ( albeit not a huge number ) is to use multiple HBAs and something like FlexRAID in software on the box. Something like these, although you can find much cheaper ones especially on ebay. These are nice because they each have 16 ports on them.

http://www.newegg.com/Product/Product.aspx?Item=N82E16816118142

You can get similar with internal and/or external ports on them as needed, but basically the idea is to parallelize some of that throughput across multiple PCIE slots. You lower the cost by not getting full on hardware RAID cards and just using HBAs and using several of them.
post #16 of 16
Thread Starter 
I'm using ZFS software RAID anyway so I'm using HBA's, not RAID cards.

I'm actually going to be using SATA disks. I'm seeing conflicting information. Others are telling me that it will be 6Gb/s x 4 lanes over the SFF-8088 cable. So 24Gb/s.
    
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