SAS 12G on a SAS 6G Backplane

[ljcool_17]

So I got curious after checking out a few server cases. Most if not all uses 6G SAS/SATA backplanes. But what if I use a SAS 12G drive on it. Will it run at 12G provided I have a 12G capable HBA (say 9300-8i) and proper cables?

[dalekphalm]

1 minute ago, ljcool_17 said:

So I got curious after checking out a few server cases. Most if not all uses 6G SAS/SATA backplanes. But what if I use a SAS 12G drive on it. Will it run at 12G provided I have a 12G capable HBA (say 9300-8i) and proper cables?

No. It will, of course, always run at the slowest link speed. Of the Backplanes are 6G, then that's the speed the entire link will be. Your drives will still work, they'll simply run at 6G instead.

 

If you want 12G, you'll need to bypass the Backplane completely, or replace it with a 12G capable backplane.

[samcool55]

Does that matter? Unless you want to use SSD's 6gbps is more than enough...

Probably not btw.

[ljcool_17]

7 minutes ago, dalekphalm said:

No. It will, of course, always run at the slowest link speed. Of the Backplanes are 6G, then that's the speed the entire link will be. Your drives will still work, they'll simply run at 6G instead.

 

If you want 12G, you'll need to bypass the Backplane completely, or replace it with a 12G capable backplane.

I see. Thank you. I was thinking maybe just bypass the backplane entirely and purchase one of these http://www.pc-pitstop.com/sas_cables_adapters/8682-05m.asp

[dalekphalm]

12 minutes ago, ljcool_17 said:

I see. Thank you. I was thinking maybe just bypass the backplane entirely and purchase one of these http://www.pc-pitstop.com/sas_cables_adapters/8682-05m.asp

You certainly could. But I would beg the question as to why you would? Would you even see a benefit? You need to build a pro/con comparison to see if you'd even max out the SAS 6G link.

 

Also, remember, with SAS, that's 6G per channel. So a normal SSF-8088 or 8087 cable, for example, is a quad-channel cable. It basically has the equivalent of 4x SAS or SATA cables inside it.

 

So if that backplane only has 4 drives plugged into it, then all 4 of those drives will essentially each get a 6G link. Furthermore, it highly depends on the drives themselves. You could easily run 6-8 (or possibly more) HDD's off of a 6G backplane without encountering bottlenecks.

 

Can you describe your intended setup, number of drives, RAID configuration (if any), etc?

[ljcool_17]

7 minutes ago, dalekphalm said:

You certainly could. But I would beg the question as to why you would? Would you even see a benefit? You need to build a pro/con comparison to see if you'd even max out the SAS 6G link.

 

Also, remember, with SAS, that's 6G per channel. So a normal SSF-8088 or 8087 cable, for example, is a quad-channel cable. It basically has the equivalent of 4x SAS or SATA cables inside it.

 

So if that backplane only has 4 drives plugged into it, then all 4 of those drives will essentially each get a 6G link. Furthermore, it highly depends on the drives themselves. You could easily run 6-8 (or possibly more) HDD's off of a 6G backplane without encountering bottlenecks.

 

Can you describe your intended setup, number of drives, RAID configuration (if any), etc?

It's for a Database server running SQL Server 2014. 12 drives, RAID 10. Was just wondering at the idea of 12G SAS. 

[dalekphalm]

1 minute ago, ljcool_17 said:

It's for a Database server running SQL Server 2014. 12 drives, RAID 10. Was just wondering at the idea of 12G SAS. 

What kind of drives? HDD?

 

SQL servers obviously like as much speed as they can get, but honestly, a 12-drive RAID 10 HDD array will likely be totally fine on SAS 6G. If you want 12G, then plan for it from the beginning, by getting a server that already has 12G backplanes - unless you can find one w/ 6G for super cheap, and also find the matching 12G Backplane upgrade (Many versions of the Dell and HP servers have the 12G upgrade option, since they use the same chassis over multiple generations).

[ljcool_17]

Setting up to get 850 Pros. I just had a Norco rep contact me and said their RPC-2212 12 Bay 2U Server Chassis does support 12G despite being mentioned to support only 6G.

[dalekphalm]

6 minutes ago, ljcool_17 said:

Setting up to get 850 Pros. I just had a Norco rep contact me and said their RPC-2212 12 Bay 2U Server Chassis does support 12G despite being mentioned to support only 6G.

Some of them may be the same as that Norco. They were likely designed before the 12G spec was finalized, but were still compatible anyway.

 

If running 850 Pro's, then certainly, 12G would be of benefit. You'd definitely want to use a kickass RAID Controller though, so that it can handle the IOPS involved here, and to make sure it was designed to be fully compatible with SSD's (Not mess up TRIM commands, for example) - I don't know if there are special considerations in this regard or not, so do your homework. And you may want to consider swapping the 850's out for actual enterprise grade SSD's - not strictly necessary, but the improved reliability may be of use.

[ljcool_17]

20 minutes ago, dalekphalm said:

Some of them may be the same as that Norco. They were likely designed before the 12G spec was finalized, but were still compatible anyway.

 

If running 850 Pro's, then certainly, 12G would be of benefit. You'd definitely want to use a kickass RAID Controller though, so that it can handle the IOPS involved here, and to make sure it was designed to be fully compatible with SSD's (Not mess up TRIM commands, for example) - I don't know if there are special considerations in this regard or not, so do your homework. And you may want to consider swapping the 850's out for actual enterprise grade SSD's - not strictly necessary, but the improved reliability may be of use.

Thank you. I am in contact with several other server case manufacturers asking them for 12G support. For now, the 850 Pro is the goal. But if I could find a good enough price for an SM863 then I would get that instead. For RAID Controller, I'm not gonna scrimp and definitely get a 9361-8i. Got a lot of favorable reviews.

[scottyseng]

6 hours ago, ljcool_17 said:

Thank you. I am in contact with several other server case manufacturers asking them for 12G support. For now, the 850 Pro is the goal. But if I could find a good enough price for an SM863 then I would get that instead. For RAID Controller, I'm not gonna scrimp and definitely get a 9361-8i. Got a lot of favorable reviews.

Also wanted to comment, please make sure to get the appropriate battery backup for the RAID card. It saves you in terms of a power loss. Curious though, why not use NVMe drives instead of RAIDing SSDs?

 

Yeah, if you're stacking the server full of SSDs, then yeah, you'd want to have a 12Gb/s backplane. Do note that while you do have eight 12Gb/s lanes, the RAID card itself has a total max speed, which may or may not bottleneck you. I remember my LSI 9260-8i tapping out at 2.2GB/s max according to a LSI technical document.