I am currently trying to figure out a performance issue with a new server compared to a old server. Performance should be better but it's not and I'm having trouble figuring out why.
Old server is a Dell R640 (2x Xeon Gold 5218, 128Gb RAM) with a PERC H740P Mini and 8Gb cache. 6x Samsung Pm1645 1.6Gb 12Gb/s SAS mixed use enterprise SSDs in a RAID 5 virtual disk
New server is a Dell R650 (2x Xeon Gold 6330, 256Gb RAM) with a PERC H755 and 8Gb cache. 6x Seagate Nytro 2532 1.92Tb 12Gb/s SAS mixed use enterprise SSDs in a RAID 10 virtual disk
The new drives are physically slower in both reads and writes but going from a 6 drive RAID5 array to a 6 drive RAID10 I thought that would make up a good deal of that. The old drives are rated at 1Gb sequential read and 1.2Gb sequential write while the new drives are at 840Mb and 650Mb. In a simple test creating a new 200Gb vhdx on both machines: the old server creates the file in about 46 seconds, the new server takes 102 seconds.
Should it really take twice as long even with the performance gain of the newer RAID? How is the old RAID5 doing it so quickly or am I just not understanding something.
Best Answer
A RAID-10 array is as fast as a RAID-0 array half its size. It can be somewhat faster than that in some configurations or for some workloads (reading alternatively from both drives of each pair). So your 6 drives RAID-10 should be 3 times as fast as one of your newer drives: 3 x 840MB/s (not Mb!) equals ~2500MB/s.
A RAID-5 array is as fast (for sequential operations only, it's much slower at random writes) as a RAID-0 with one less drive. So your 6 drives RAID-5 should be 5 times as fast as your older drives: 5 x 1GB/s = 5 GB/s. Which is about twice as fast as your newer setup, and match quite well your numbers.