achieving good LTO 4 speed

Currently building a server to host some direct attached storage to stream to the LTO4 that's connected to the same box via U320 cable, via Commvault.

I can't find any stats on the disks MB/sec performance so, do i buy 14 performance disks for 7TB or will the 2TB disk be able to supply a fast enough stream to the LTO4 to achieve 180MEG/sec

the server will be a brand new DL360 g6, how does one work this out?

12 x 600 GB 6G 15K LFF Dual-port ENT SAS


12 x 2 TB 6G 7.2K LFF Dual-port MDL SAS

Obviously if the 2TB drives can achieve a good MB/sec stream to the LTO4 I'd prefer the larger space they provide.
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Either solution is capable of pumping that much I/O, if it is configured properly.   Make sure the LTO4 is using a PCIe controller, not PCIx.  Many things will make or break the configuration, and the specifics of how you configure the RAID, your choice of O/S, and filesystem parameters are vital.

The key is to keep it streaming instead of going into a stop start mode, you want to insure that the storage pool for the tape is not wasting a lot of precious I/Os handling things like the operating system itself.  

One big problem is that you had better be doing RAID6 on the 12+2, it will take DAYS to rebuild after a drive failure, if the system is busy, it might take a week.  Do you want to risk a 2nd failure?

So if you have RAID6, then optimal configuration is going to be 10 disks total.  Optimal for RAID5 is 9 disks.    Use the other disks to build a RAID1 for the O/S.  Use the other disk as a hot spare.
MC2010Author Commented:
this disk library will be for backups only. and be windows. client to disk will be different window from the to tape, so there will only ever be one stream running when running to tape, OS will be on a internal mirror 15k raid.
Gerald ConnollyCommented:
So the LTO4 runs at 120MB/sec, that shouldnt be a problem from either of those two disk setups. With the speed of modern drives, achieving 11MB/sec per drive (RAID-5 11+1) or 12MB/s (10+2)  even with a 7.5K drive is not a problem
I have always used a disk throughput of  2-3 times tape speed to ensure that the tape drive cache is kept full and therefore the tape will stay streaming with no chance of  shoe-shining as thta is what kills the performance. That means 24-36MB/s per drive still shouldnt trouble them.

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andyalderSaggar maker's framemakerCommented:
I agree the 7.2k disks will be fine as long as the disk staging area does not become defragmented since you'll be doing sequential reads and writes rather than randon I/O.
MC2010Author Commented:
thank you this seals it for me
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