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I have a RAID 10 array with four 1TB WD RE4 drives SATA II. The OS is installed on it and our accounting software (SAGE 50).

I was considering adding two 256GB SSD's in RAID 1 to store the data from SAGE 50.

Would the application benefit from the SSD speed where data is stored, given that the application installed on the slower RAID?

Note: The RAID 10 controller only supports 4 drives.

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2 Answers 2

Are you experiencing any performance issue with your current RAID 10 setup? You will only see performance increase if your 2 x 256GB SSD are faster and configured correctly on high end of RAID card.

Also, try to choose correct SSD, MLC or SLC, based up on the performance you are getting with WD RE4 drives. Also, if you haven't enabled 'Write Cache' on your RAID controller, try to do so (if you have a BBU). That will increase the performance. Below link might be helpful to you:

http://www.computerweekly.com/feature/MLC-vs-SLC-Which-flash-SSD-is-right-for-you

If you can post the exact specification of your server, I might be able to help further.

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I'm using Adaptec 6405 RAID controller and getting READ WRITE SEQ 437.3 266.2 512K 77.63 140.5 4K 0.939 3.684 4K QD32 6.581 3.877 and the RAID 1 SSD's are getting 40% faster read speeds and increased write speeds. So the RAID 1 setup will be faster, but I'm more concerned if the application will benefit from the data being on the RAID 1 even though the application is on the RAID 10. SSD's are MLC, 256GB. Write cache is enabled. –  NoMoreDell4Me Nov 13 '12 at 14:46

How much benefit (if any) you see depends on the workload and I/O profile.
You need to do an analysis and determine what makes sense.

  • If the application spends a lot of time reading its executables and libraries you want to put the application itself on the SSDs.

  • If the application spends a lot of time reading data files you want to put the data files on SSDs.

  • If the application spends a lot of time doing read/write I/O to its data files you want to determine of the SSD's write speed will be an issue (if the SSD write speed is as good or better than rotating disk you can see a performance benefit, but if you spend a lot of time writing data and the SSDs take longer to do that you may see a performance decrease)


Also note that if you're not saturating your disk's I/O bandwidth (hitting the disk's limits) SSDs may not give you a meaningful performance increase at all: You can read data faster than spinning disks can, but if you don't actually need that speed the performance improvement will be negligible.

Similarly if your disks are saturating your controller's bus SSDs won't help (the SSDs will also saturate the controller's bus, and you'll see identical performance) -- SSD or spinny disk your limit is still the controller.

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