Upgrading from SAS 6G to SAS 12G

FrozenSteel

Limp Gawd
Joined
Oct 24, 2011
Messages
193
Hey guys, here's a question. I have a server with an LSI 9260-8i controller that connects to a backplane that supports 8x2.5 inch drives in the front of the server via two SFF-8087 to SFF-8087 miniSAS cables. If I get an Adaptec 8885 controller and use two SFF-8643 miniSAS HD to SFF-8088 miniSAS cables, and use a 12G SAS SSD, will everything run at SAS III (12G)? Getting deep into it, the only SAS II piece is the backplane and all it does is route wires from the cable to the drives, there's no logic there at all. Thoughts?
 

ToddW2

2[H]4U
Joined
Nov 8, 2004
Messages
4,018
It will not make an 8087/8088 run at 48Gb/s.

8087 / 8088 have a max throughput technically of 4x 6Gb/s channels that's 24Gb/s.
You aren't going to get 4x 12Gb/s from them.
Just like his backplane is not going to jump to 12Gb/s per-channel.

Now, maybe if it was a direct attach backplane and he went from the Adaptec 8885 to 12Gb/s fan-out cable to direct-attach backplane he MIGHT be able to get > 6Gb/s. This would obviously require a lot more cards, and cables, and be a lot more of a mess but some people have reported this working on 3Gb/s and getting 6Gb/s... but I don't know the specifics to that or if it could work from 6 to 12.

You basically have 3 types of backplanes that offer different performance levels to a certain degree.
- Expander (and Dual expander)
- Multilane (I believe that's what they call having an 8087 or miniSAS connections per-4 drives on the backplane)
- Direct Attach (1 Cable In : 1 Connection To HD/SSD)

If you want to get the absolute highest performance then direct attach is it but a huge cable mess, most end up going with multi-lane since it's not much < than direct.

And then the backplanes are rated SAS SASII SASIII

I'm not sure if direct attach have that rating though, and why it may work in some cases at the 'new' speed.
 
Last edited:

SomeGuy133

2[H]4U
Joined
Apr 12, 2015
Messages
3,447
It will not make an 8087/8088 run at 48Gb/s.

8087 / 8088 have a max throughput technically of 4x 6Gb/s channels that's 24Gb/s.
You aren't going to get 4x 12Gb/s from them.
Just like his backplane is not going to jump to 12Gb/s per-channel.

Now, maybe if it was a direct attach backplane and he went from the Adaptec 8885 to 12Gb/s fan-out cable to direct-attach backplane he MIGHT be able to get > 6Gb/s. This would obviously require a lot more cards, and cables, and be a lot more of a mess but some people have reported this working on 3Gb/s and getting 6Gb/s... but I don't know the specifics to that or if it could work from 6 to 12.

You basically have 3 types of backplanes that offer different performance levels to a certain degree.
- Expander (and Dual expander)
- Multilane (I believe that's what they call having an 8087 or miniSAS connections per-4 drives on the backplane)
- Direct Attach (1 Cable In : 1 Connection To HD/SSD)

If you want to get the absolute highest performance then direct attach is it but a huge cable mess, most end up going with multi-lane since it's not much < than direct.

And then the backplanes are rated SAS SASII SASIII

I'm not sure if direct attach have that rating though, and why it may work in some cases at the 'new' speed.

ah cool thanks for all that info!
 

izx

Limp Gawd
Joined
Jul 30, 2007
Messages
308
8087 / 8088 have a max throughput technically of 4x 6Gb/s channels that's 24Gb/s.

No, technically their max throughput is 10Gb/s/channel (source: official standard.

Also, some cable manufacturers, specifically Molex, appear to be comfortable rating their SFF-8087/8088 to perform at SAS3/12 GBps speeds.

...backplane that supports 8x2.5 inch drives in the front of the server via two SFF-8087 to SFF-8087 miniSAS cables.

OK, so that's a dumb (multi-lane) backplane. Know the SFF-8087 to 4xSATA cables? That's what the backplane does, only it does it on its PCB on the way from the SFF-8087 connector the 4xSATA drive connectors.

If I get an Adaptec 8885 controller and use two SFF-8643 miniSAS HD to SFF-8088 miniSAS cables, and use a 12G SAS SSD, will everything run at SAS III (12G)? Getting deep into it, the only SAS II piece is the backplane and all it does is route wires from the cable to the drives, there's no logic there at all. Thoughts?

In theory, it should work. In practice, it may work, depending on the quality of the backplane interconnects. Who is the backplane manufacturer?

Consider the Supermicro BPN-SAS-846A backplane, which supports 24-drives via 6 iPass connectors. Supermicro did not release SAS2 or SAS3 versions of this backplane, and there are multiple forum reports of the backplane working just fine at SAS2 speeds.
 

staticlag

[H]ard|Gawd
Joined
Mar 26, 2010
Messages
1,679
Yes in theory it might work. Depends on the level of interference the cable/backplane receives. It will try sas 3, if it senses errors it will downgrade the link speed. Just the same as sata, ethernet, fiber, etc...
 

FLECOM

Modder(ator) & [H]ardest Folder Evar
Staff member
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Jun 27, 2001
Messages
15,739
might work, I would just watch the error rate... a fanout is really no different than letting the backplane fan out 8087 connectors

if there is no expander the backplane should just pass whatever... if it will meet the specs of what you are trying to pass is the question, and there is really no way for any of us to answer that
 
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