[RndTbl] poor drive/array performance

[Trevor Cordes]

I have an new SSD in a system setup as linux md RAID-1 but with the 2nd 
drive missing at the moment.  No LVM.  FS is ext4, very recently created 
and less than half full.  ext4 creation had no tweaks (just default 
options).  md creation had no tweaks.

I'm getting extremely bizarre low FS performance.

cd /tmp
dd if=/dev/zero of=zzzz conv=fdatasync bs=1M count=250
262144000 bytes (262 MB) copied, 21.3281 s, 12.3 MB/s
again...
262144000 bytes (262 MB) copied, 35.6929 s, 7.3 MB/s
again...
262144000 bytes (262 MB) copied, 26.1413 s, 10.0 MB/s

This SSD is rated at 450MB/s write.  Sites on the net say I may only 
realize 100MB/s.  I would be overjoyed with 100MB/s.  I'm not looking for 
blazing speed, just not garbage speed.

The system had a rust drive previously that had the same problem.  When I 
replaced that, I also recreated the RAID, and the FS.

Strangely, this drive is also part of another array for /boot, and that 
one has 2 drives, one of them spinning rust.  And that array/FS is 
faster!?  Huh? :
262144000 bytes (262 MB) copied, 14.6355 s, 17.9 MB/s
262144000 bytes (262 MB) copied, 13.4979 s, 19.4 MB/s
262144000 bytes (262 MB) copied, 9.99149 s, 26.2 MB/s

I'm baffled.  I really am.

hdparm's speed tests show it to behave super fast for reads:
 Timing buffered disk reads: 1010 MB in  3.00 seconds = 336.32 MB/sec
 Timing cached reads:   26774 MB in  2.00 seconds = 13412.64 MB/sec

I've checked hdparm -i:
 Model=KINGSTON SV300S37A480G, FwRev=603ABBF0, SerialNo=50026B7763021118
 Config={ HardSect NotMFM HdSw>15uSec Fixed DTR>10Mbs RotSpdTol>.5% }
 RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=4
 BuffType=unknown, BuffSize=unknown, MaxMultSect=1, MultSect=1
 CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=937703088
 IORDY=on/off, tPIO={min:120,w/IORDY:120}, tDMA={min:120,rec:120}
 PIO modes:  pio0 pio1 pio2 pio3 pio4 
 DMA modes:  mdma0 mdma1 mdma2 
 UDMA modes: udma0 udma1 udma2 udma3 udma4 udma5 *udma6 
 AdvancedPM=yes: unknown setting WriteCache=enabled
 Drive conforms to: unknown:  ATA/ATAPI-2,3,4,5,6,7

udma6 is the correct mode for something like this I do believe.

smartctl shows correct sata speeds:
ATA Version is:   ATA8-ACS, ACS-2 T13/2015-D revision 3
SATA Version is:  SATA 3.0, 6.0 Gb/s (current: 6.0 Gb/s)

Kernel is fairly new:
4.4.6-200.fc22.i686+PAE

Hardware is server class Intel Xeon E3 with S1200V3RP board, a fairly new 
model.

My only thoughts now are firmware problems, bios setting problems, or 
cable problem.  I need to go onsite to check all three.

Anything I am missing?  I have lots of extremely similar systems out there 
*without SSDs* and they all show FS write speeds of no slower than 60MB/s!  
Weird!!