Crucial MX500 + Perc H700

Kilobyte Kid

Crucial MX500 + Perc H700

Hello,

 

Poor performance of disks on the RAID controller Perc H700.

 
# dd if=/dev/zero of=/mnt/sda/tempfile count=64k bs=32k conv=fdatasync && rm -f /mnt/sda/tempfile
65536+0 records in
65536+0 records out
2147483648 bytes (2.1 GB) copied, 8.07634 s, 266 MB/s
# dd if=/dev/zero of=/mnt/sda/tempfile count=1M bs=2048 conv=fdatasync && rm -f /mnt/sda/tempfile
1048576+0 records in
1048576+0 records out
2147483648 bytes (2.1 GB) copied, 9.40265 s, 228 MB/s
 

# megacli  -LDInfo -Lall -Aall


Adapter 0 -- Virtual Drive Information:
Virtual Drive: 0 (Target Id: 0)
Name                :Virtual Disk 0
RAID Level          : Primary-1, Secondary-0, RAID Level Qualifier-0
Size                : 931.0 GB
Sector Size         : 512
Mirror Data         : 931.0 GB
State               : Optimal
Strip Size          : 64 KB
Number Of Drives    : 2
Span Depth          : 1
Default Cache Policy: WriteThrough, ReadAheadNone, Direct, Write Cache OK if Bad BBU
Current Cache Policy: WriteThrough, ReadAheadNone, Direct, Write Cache OK if Bad BBU
Default Access Policy: Read/Write
Current Access Policy: Read/Write
Disk Cache Policy   : Enabled
Encryption Type     : None
Bad Blocks Exist: No
Is VD Cached: Yes
Cache Cade Type : Read Only

 
How to increase speed?
5 Replies
JEDEC Jedi

Re: Crucial MX500 + Perc H700

It is a limitation of the TLC NAND technology.    TLC drives are meant for average consumer use (meaning small amounts of writing, but lots of reading).    I actually had an MX300 (uses TLC NAND)  and I tested it over USB3.  It will go at near 500MB/s for 30-40 seconds until the cache is filled, then it drops to about 250MB/s.   As I continued testing the MX300 eventually dropped until a spinning hard drive is faster.   In fact the MX300 actually got locked into the lower speed of 50MB/s and the only way I could recover it was by a Secure Erase.   I tried several MX300s to be sure it was not a bad drive.   This was before websites were giving proper true reviews of the TLC SSD performance.  I believe I read that the TLC  SSDs may also be throttled when the temperatures rise, but I'm not sure if that is correct. 

 

Do the test again, but use   dstat   to monitor the SSD while you do the "dd" test.     

Use:   dstat  -tdD    sda      

 

I understand the MX500 should be better than the MX300s due to some design changes, plus they are using a different controller.  Personally I'll stick to the MLC SSDs for as long as possible.  Surprisingly the BX300 series uses MLC NAND.   

 

Here is an very good article on Tom's Hardware giving the current status of SSD technology.

Kilobyte Kid

Re: Crucial MX500 + Perc H700

This problem is only when using disks with the controller Perc H700, without it the performance are much higher.
Highlighted
JEDEC Jedi

Re: Crucial MX500 + Perc H700

Does it have a cache?  We're testing my memory here (never a good thing!) but at least in the olden days SSD performance was terrible on 'proper' RAID controllers that lack a cache...

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Kilobyte Kid

Re: Crucial MX500 + Perc H700

Yes, there is, 512 MB.
Turning on or off the cache in a RAID controller has almost no effect on performance.
Bit Baby

Re: Crucial MX500 + Perc H700

I have the same problem, it does not just happen on the raid dell perc h700, which also happens on the IBM m5015 raid, and I think it also happens on many other raid cards.

 

And this makes any operation on the SSD drive worse. Sequential read speed is 7k2 rpm (~ 200mb / s) SATA drive, and fio tests are really pathetic (about a few thousand points).

 

I bought five new Crucial MX500 SSDs, but I really did not know what to do with them because my server used the Dell Perc H700 raid card and the IBM M5015 did not recognize them as SSDs. They only make them corrupt. and does not guarantee stable operation of the server.

 

This is a real deadlock, so let my servers know that they are working with Crucial SSD drives?