Can a RAID Array straddle multiple caddies

[Kev Swindells]

Hi,

I have a ML370 G6 which currently has two hard disk caddies installed in it - once of which has four disks installed and configured as a RAID array.

I wish to increase the capacity of this and wish to install a further five drives - however the caddie only has four slots remaining.

If I install the five drives across two caddies can the server still RAID them together, and if so is there any performance impact?

[TTr · Accepted solution]

Assuming you have the built-in raid controller, P410i, it only has 8 SAS ports. So you can not connect to both disk cages.

The only way you can connect to the 2nd cage is by a second raid controller, P410, or by adding a SAS expander card. Adding disks to a controller always impacts performance but it all depends on your i/o requirements.
Adding a second P410 would give you faster i/o but the two raid controllers are independent of each other you can not create raid arrays across the cages/controllers.

With a SAS expander card all disks would attach to the same controller and you could create large arrays with many disks. I/O is impacted but if you don't have high i/o demand it will be fine.

http://h18000.www1.hp.com/products/servers/proliantstorage/arraycontrollers/sas-expander/index.html

[Kev Swindells]

Hi, Thanks for that TTR.

We do have an SAS Expander card installed in the server.

[TTr]

In that case you can wire both cages to the SAS expander card and then the exp card back to the P410i.

The SAS expander card takes the 8 ports from the P410i and switches them out to the 16 ports of the two cages, so there is switching taking place like in a LAN switch.

As I said before it depends on your i/o requirements. In your case with only two arrays the switching over to the second cage is not going to impact the i/o. If you add more disks and you fill up both cages you might notice some more impact to the i/o.