DL560 Gen8 SAS ports question

[Cederberg]

Hi.

I have a question that came to mind when we bought the new dl560 gen8. It has 5 drive slots  the first four slots goes to port 1 on the raid card and only the fith goes to port 2.

Historically on our dl380 platforms we have spread the "OS drive" with a mirror over the two channels and a hot spare. for example our dl380 standard has 1 drive in port 1 bay 1 wich is mirrored with port2 bay 5 and the hot spare we usualy place in the last slot port 2 bay 8. We have done so for the redundancy (if one channel breaks we still have a disk online).

As the DL560 gen8 has only one drive on port2 it got me thinking what is the recommeded way of doing this and what gives the best performance and redundancy?

best regards

//Cederberg

[gregersenj]

I have not studiet this carefully. But here's a link, to start with:

http://h20000.www2.hp.com/bc/docs/support/SupportManual/c01460725/c01460725.pdf

I do remember the past, as you describe.

BR

/jag

[Cederberg]

Thanks for the link didn't say much in there but lead me to another document that at least mentioned the SAS channels.

http://h20000.www2.hp.com/bc/docs/support/SupportManual/c02249094/c02249094.pdf

It says that for performance it can be better to split between the channels if you have a lot of drives. As for my example above it has little to no importance performance wise. Wasn't able to find any thing about the redundancy part. But if i apply some degree of logic, it make sense that one channel could "break" and i still have a channel up. The probability for that to happen? well i don't know.

[gregersenj]

Yes, there's a lot good links, in that documents, and if you follow them all, you will learn a lot.

The SAS and SATA protocol is a point to point protocol.

So there's one connection to each device. So basically it is redundant. 

Well until you add a SASS switch.

If you got a smart array P410, you will find 2 connetors, with 4 connections each. That is 8 separate connections for 8 devices. They do share cables and connectors, but the wires are there.

You can choose to split your drives over 2 cables, like you used to do in the past.

BR

/jag