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October 11th, 2013 13:00
SAS 6/iR disk configuration options
I need to add storage to a PE 2900 with a SAS 6/iR integrated controller. Two drive bays have 1Tb disks raid 1 for the OS. I want fill the remaining six bays with disks, but am not sure how they can be configured. The controller only supports raid 0 and 1, and a maximum of two virtual disks. Is it possible to configure the six new disks using raid 1 - will it group the disks in three and three, then mirror those two groups?
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theflash1932
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October 11th, 2013 14:00
No, it is not a supported config on any Dell controller (although you can tweak it out on the older controllers). The SAS 6 is a low-end controller, capable ONLY of RAID 0 and 1 (not 10 or any other "nested" RAID level).
"If I plugged six 1Tb disks in, can you estimate how much storage I could realize without resorting to JBOD and individual drive letters?"
Without resorting to JBOD, the math is simple:
Redundant: 2x1TB RAID 1 = 1TB (930GB after disk math)
Non-redundant: 6x1TB RAID 0 = 6TB (5.6TB after disk math)
Obviously, the redundant option does not "net" you a lot of space, and the non-redundant option is, well, not redundant.
Mixing hardware and software RAID is not advisable when redundancy is partially dependent on one or the other, but you could stripe 3 on the controller, stripe 3 in the OS, then mirror hw R0 with sw R0 in the OS (2.8TB usable space), but then I think you over-complicate things for Windows and likely sacrifice too much performance - and possibly reliability. You could do JBOD and let Windows manage them all in a software RAID 5 (4.6TB).
PCC Bob
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October 11th, 2013 14:00
Agreed - mixing hardware & software raid does not sound viable. I was getting so wrapped up in the hardware side, I didn't think about just using Windows to manage the disks with Raid 5 ... that sounds like the best solution at this time. Thanks for your input!
PCC Bob
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October 11th, 2013 14:00
Yes, raid 0+1 is what I was thinking when I described the two groups of three disks. This is not a supported configuration with this controller? Replacing the controller with a PERC is not a viable option at this time.
It sounds like I may have to use Windows for mirroring the disks (Server 2008 R2) I would like to keep the number of drive letters presented to the OS as few as possible, and still retain redundancy whether it's hardware raid or software raid. If I plugged six 1Tb disks in, can you estimate how much storage I could realize without resorting to JBOD and individual drive letters?
This storage will be used for Backup Exec D2D storage and some near-line data storage - performance is not critical but some redundancy is required.
theflash1932
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October 11th, 2013 14:00
The SAS 6 also supports non-RAID configurations. You have only four options:
"Is it possible to configure the six new disks using raid 1"
RAID 1 requires exactly two disks.
"will it group the disks in three and three, then mirror those two groups?"
This would not be called RAID 1, nor would it be considered a RAID 10 - it would be a RAID 0+1. With a PERC 6 (instead of a SAS 6), you could configure six disks in a RAID 10 or 50. RAID 10 would pair the disks into 3 mirrors, striping the data across them. RAID 50 would group each set of 3 disks in a RAID 5, striping data across them.