True. The majority of the time the disk I/o will be at a Queue Depth of 1, because you just wont be generating the workload to get higher, which means you will be at pretty much the lowest write performance for the SSD, and it will probably be 4k random writes, which is usually the lowest performing write type; although, ideally, you are running a block size that matches your stripe size, you have sized your stripe to the workload you are running**, and you have aligned the volumes correctly, as not doing so can significantly affect performance, and in some cases, defeat the purpose of striping data across disks.It's probably worth noting that in my testing (I'd say experience, but the amount of back and forth and try-this-then-try-that amounts to testing), the benefits of any striped RAID with SSDs is that you greatly improve the poor small-file-write performance. I've seen this have a dramatic effect on things like logging out of one group of toons and into another, or speeding up quick-saves in single-player games like Half Life, Shadow Warrior, etc. I had better write/save speeds with two 840 Pros than I did with a single 950 Pro.
** High performing RAIDs are effective for a given type of workload. It usually requires in depth knowledge about the services that you are hosting in the enterprise world where you are planning single task servers. Home systems are just a PITA with their multiple usage scenarios, and don't translate very well to a high performance RAID design. This is not to say a home system wont benefit from a stripe, it just wont be as effective.
So, yes, having 2 disks to write half the data to will always be faster, unless the single disk write random performance is faster. If it fairly simple enough to show this with some simple stats and easy math.
This is a simplistic view as chances are you are not really writing 4k writes all the time, it will vary depending on many factors, but it is easy to show the worst case scenario, and the improvement you get from it when using RAID0.
For eg.
an 840 PRO (256GB), has a random write @ 4k, of approximately 33000 IOP's,
an 850 EVO (250GB) , has a random write @ 4k, of approximately 40000 IOP's,
a 950 PRO (256GB), has a random write @ 4k, of approximately 57000 IOP's,
So two 850 EVO's in a raid 0 will have an effective comparable rate of 80000 IOP's, two 840 PROs 66000 IOP's, hence both are faster, for 4k random writes than a single 950 PRO.
Note: depends on firmware for the drives too, the 840 PRO's original firmware was around 15k IOP's @ 4k random writes.
Comes down to the problem you are trying to solve, and whether the solution is worth it, to you, for the money you need to spend.
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