Poor hard drive performance

Question

I have nearly two identical servers, the only difference between the two is the version of Linux and the Hard Drive. Server 1 had (what I think) is a better drive, therefore the performance should be better then what I'm seeing compared to Server 2. Most notably is the difference between the dd test on server 1 and 2 as seen below.

Any suggestions on what to check and what would cause this?

Server 1:

Drive is a Barracuda 7200.12 SATA 6Gb/s 1TB Hard Drive w/64 MB Cache Running XenServer, test performed @ the non-guest level.

hdparm -i /dev/sda

/dev/sda:

 Model=ST31000524AS                            , FwRev=JC4B    ,
SerialNo=            5VP9RWSG
 Config={ HardSect NotMFM HdSw>15uSec Fixed DTR>10Mbs RotSpdTol>.5% }
 RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=4
 BuffType=unknown, BuffSize=0kB, MaxMultSect=16, MultSect=?16?
 CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=268435455
 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
 AdvancedPM=no WriteCache=enabled
 Drive conforms to: unknown:  ATA/ATAPI-4 ATA/ATAPI-5 ATA/ATAPI-6 ATA/ATAPI-7

hdparm -tT /dev/sda

/dev/sda:
 Timing cached reads:   43912 MB in  1.99 seconds = 22043.28 MB/sec
 Timing buffered disk reads:  344 MB in  3.00 seconds = 114.64 MB/sec

dd if=/dev/zero of=/tmp/output.img bs=8k count=256k

262144+0 records in
262144+0 records out
2147483648 bytes (2.1 GB) copied, 28.0981 seconds, 76.4 MB/s

/etc/fstab

LABEL=root-rizocqaz    /         ext3     defaults   1  1
/var/swap/swap.001          swap      swap   defaults   0  0
none        /dev/pts  devpts defaults   0  0
none        /dev/shm  tmpfs  defaults   0  0
none        /proc     proc   defaults   0  0
none        /sys      sysfs  defaults   0  0

Server 2:

Drive is a Hitachi Deskstar 7200 SATA 3Gb/s 1TB Drive w/32 MB Cache Running Debian 6

hdparm -i /dev/sda

/dev/sda:

 Model=Hitachi HDS721010CLA332, FwRev=JP4OA3MA, SerialNo=JP2940HZ3L08GC
 Config={ HardSect NotMFM HdSw>15uSec Fixed DTR>10Mbs }
 RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=56
 BuffType=DualPortCache, BuffSize=29999kB, MaxMultSect=16, MultSect=16
 CurCHS=65535/1/63, CurSects=4128705, LBA=yes, LBAsects=1953525168
 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: disabled (255) WriteCache=enabled
 Drive conforms to: unknown:  ATA/ATAPI-2,3,4,5,6,7

dd if=/dev/zero of=/tmp/output.img bs=8k count=256k

262144+0 records in
262144+0 records out
2147483648 bytes (2.1 GB) copied, 13.0055 s, 165 MB/s

hdparm -tT /dev/sda

 Timing cached reads:   24350 MB in  2.00 seconds = 12191.54 MB/sec
 Timing buffered disk reads: 418 MB in  3.00 seconds = 139.22 MB/sec

/etc/fstab

proc            /proc           proc    defaults        0       0

UUID=7fcbd976-2dbc-43fb-a321-2dfd5bc0ff4f /               ext3    errors=remount-ro 0       1
UUID=b3a09499-a85e-4b6c-a6e5-14586861c347 none            swap    sw              0       0

Answer 1

The linear throughput of a disk deteriorates as the magnetic tracks spiral further to the disk's center:

This is simply due to the fact that the linear velocity there is much lower than in the outer parts of the rotating disk.

Since you do not know on which part of the disk the blocks of /tmp/output.img are ending up, your comparison of "dd" results is pointless. In contrast, the "hdparm" test always does read the first blocks of the disk - this is why you see more consistent results there.

Anyway, the results will vary as there likely is some concurrency in disk activity while your systems read and write the disk while you are measuring.