SAS multipath + load balancing using one RAID card

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ymc

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May 13, 2010
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Dear all,

This LSI doc's page 6 suggests that it is possible to set up a multipath and load balanced SAS array using one RAID card:

http://www.lsi.com/DistributionSystem/AssetDocument/ESG_MR_SeagateES.2SAS_WP_Seagate.pdf

How do you think this is done???

Suppose I have one LSI 9260-8i and four dual port SAS drives. How to set this up?

Will this set up work?
1) Buy two SFF-8087 to 4x SATA cables.
2) Connect the two SFF-8087 ends to 9260-8i
3) Buy four dual port backplanes for the four dual port SAS drives
4) Connect four SATA ends of each cable to all four different backplanes. Repeat this for the other SAS cable.

Thanks in advance!
 
No one knows? Supposedly this setup can increase the performance substantially accroding to that pdf. Can a SAS people here gives it a try????
 
I think in the particular setup you are considering, there would be no performance benefits.

You are correct that you could get two paths to each drive, which helps with redundancy should one of the physical connections have a problem.

However, the benefits of load balancing would only be realized in the case where you would configure two x4 wide ports to one or more enclosures with a SAS expander. In this case you could designate one of the x4 ports to handle a certain subset of drives within an enclosure and the second x4 port to handle the remaining drives. This way you can share the bandwidth of both SAS x4 links across all the drives.

The setup you propose has a limitation due to the fact that when you connect a single initiator to both ports of a dual-port target drive, only one of the ports on the drive can be active at a single time.

But the reality is that with only a single drive on each SAS port you don't need to worry about load balancing since each drive has a dedicated path to the controller in that case. You won't see any current hard drive saturating a 6gb/s link.
 
UICompE02 said:
I think in the particular setup you are considering, there would be no performance benefits.

You are correct that you could get two paths to each drive, which helps with redundancy should one of the physical connections have a problem.

However, the benefits of load balancing would only be realized in the case where you would configure two x4 wide ports to one or more enclosures with a SAS expander. In this case you could designate one of the x4 ports to handle a certain subset of drives within an enclosure and the second x4 port to handle the remaining drives. This way you can share the bandwidth of both SAS x4 links across all the drives.

The setup you propose has a limitation due to the fact that when you connect a single initiator to both ports of a dual-port target drive, only one of the ports on the drive can be active at a single time.

But the reality is that with only a single drive on each SAS port you don't need to worry about load balancing since each drive has a dedicated path to the controller in that case. You won't see any current hard drive saturating a 6gb/s link.
Click to expand...

Thanks for your reply. I think it makes sense.

So how do you setup a system that can see real performance gain? Do you think the setup below with 12 drives with an expander can do this?

1) Buy two SFF-8087 to SFF-8087 mini SAS cables
2) Buy six SFF-8087 to 4x SATA cables.
3) Buy one HP 36 ports SAS Expander
4) Connect the two SFF-8087 to SFF-8087 cables one end to 9260-8i and one end to HP SAS Expander
5) Connect the six SFF-8087 to 4x SATA cables to the HP SAS Expander
6) Buy 12 dual port backplanes for the 12 dual port SAS drives
7) Any two of the SFF-8087 to 4x SATA cables will be responsible for four drives. Connect four SATA ends of each cable to four different backplanes. Repeat this for the other SFF-8087 to 4x SATA cable.
8) Repeat 7) for other eight drives.
 
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