The Meaning of this Crystal Disk Mark Score from my RAID 5?

[Ben Jobe]

I recently set up an (8) 6TB disk RAID 5 array inside my PC tower using an LSI MegaRAID 9361-8i card. After waiting 7 days for a full NTFS format to finish, I ran Crystal Disk Mark and got these results:

READ
Seq. Q32T1: 1452 MB/s
4K Q32T1: 11 MB/s
Seq.: 1044 MB/s
4K: 0.77 MB/s

WRITE
Seq. Q32T1: 1338 MB/s
4K Q32T1: 5.2 MB/s
Seq.: 77 MB/s
4K: 0.97 MB/s

Now I definitely like the Seq. Q32T1 scores. But the rest of it looks awful.

I then moved 12TB of data onto the array and ran the Crystal Disk Mark tests again. Here's what I got:

READ
Seq. Q32T1: 301 MB/s
4K Q32T1: 11 MB/s
Seq.: 102 MB/s
4K: 1.1 MB/s

WRITE
Seq. Q32T1: 126 MB/s
4K Q32T1: 5.4 MB/s
Seq.: 56 MB/s
4K: 1.5 MB/s

Now all of the scores look awful.

I've tried using different settings for the LSI MegaRAID card like Read Ahead / Write Through / Cached / Direct. None of them make a big difference.

My best guess is that I set the RAID Stripe Size and the NTFS File System Allocation Unit Size too large. (I did this because the drive contains mostly HD and 4K video files)

Stripe Size: 256 KB
Allocation Unit Size: 32 KB

Does anyone have any thoughts on this?

 

[gaborbarla]

Hi, the 4k reads are low beacause the drive heads need to jump around to fetch the file located on different parts of the drive. That is where SSDs really shine and can outperform normal drives many many times over. The sequential reads in the second test are a bit odd, but when you put 12tb of data perhaps the drive fragmented a bit and maybe this now affects sequential read performance.