On 12/12/2011 11:54, Jan Kasprzak wrote:
Hello, Linux RAID gurus, I have a new server with two identical external disk shelves (22 drives each), which will be connected to the server with a pair of SAS cables. I want to use RAID-10 on these disks, but I want it to be configured so that the data will always be mirrored between the shelves. I.e. I want to be able to overcome complete failure of a single shelf. Is there any way how to tell mdadm explicitly how to set up the pairs of mirrored drives inside a RAID-10 volume?
If you're using RAID10,n2 (the default layout) then adjacent pairs of drives in the create command will be mirrors, so your command line should be something like:
# mdadm --create /dev/mdX -l10 -pn2 -n44 /dev/shelf1drive1 /dev/shelf2drive1 /dev/shelf1drive2 ...
Having said that, if you think there's a real chance of a shelf failing, you probably ought to think about adding more redundancy within the shelves so that you can survive another drive failure or two while you're running on just one shelf.
If you are sticking with RAID10, you can potentially get double the read performance using the far layout - -pf2 - and with the same order of drives you can still survive a shelf failure, though your use of port multipliers may well limit your performance anyway.
Hope this helps! Cheers, John. -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
