[CentOS] Extremely slow disk transfers with SATA disks

Vanja Hrustic vanja at pobox.com
Thu Mar 23 14:37:49 UTC 2006


I have installed CentOS 4.2, recently, on new computer.

Everything seemed to work fine.

However, we've found out that disk transfers are incredibly slow, and I
just can't figure out what to do in order to fix it.

Computer is now running CentOS 4.3 (updated it 1 hour ago), and same
thing is still present. I hoped kernel upgrade might fix it, but it
didn't.

Computer has 2 SATA disks, 200GB (Maxtor 6Y200M0) and 80GB (Maxtor
6L080M0).

There are no errors or any other indications of problems in logs/dmesg.

Copying 500MB file takes around 210 seconds. Around 2.3MB/sec.

Doesn't matter if I am copying from one hard disk to another, or onto
the same hard disk.

When copying, vmstat shows:

 r  b   swpd   free   buff  cache   si   so    bi    bo   in    cs us sy id wa
 0  0    160 525928   1060 278044    0    0  1609  1112 1387  1146  9  4 39 47
 0  0    160 525928   1060 278044    0    0     0     0 1084   745  0  0 100  0
 0  0    160 525844   1060 278044    0    0     0     0 1067   795  2  0 98  0
 0  0    160 525844   1060 278044    0    0     0     0 1084   745  1  0 99  0
 0  0    160 525844   1072 278044    0    0     0   156 1073   757  0  0 100  0
 0  1    160 525564   1148 278228    0    0   240     0 1129  1136  2  1 77 20
 0  1    160 522708   1176 281256    0    0  1600     0 1283  1155  0  2  0 98
 0  1    160 519380   1184 284568    0    0  1672     0 1327  1231  0  2  0 98
 3  1    160 516404   1196 287368    0    0  1412     0 1264  1126  1  1  0 98
 0  1    160 513524   1196 290424    0    0  1536     0 1353  1926 11  2  0 87
 0  3    160 510132   1208 293544    0    0  1544  7348 1407  2163 24  6  0 71
 0  1    160 513780   1216 289972    0    0  1412   140 1360  1536  9  3  0 88
 2  0    160 515316   1220 288464    0    0  1104     0 1341  2067 47  4  0 49
 0  1    160 518996   1216 284608    0    0  1712     0 1333  1676 34  7  0 59
 0  1    160 516820   1224 286832    0    0  2052     0 1318  2025 25  4  0 71
 1  2    160 512388   1228 291024    0    0  2952  8736 1433  1431  6  4  0 90
 2  1    160 504772   1244 295304    0    0  3076    76 1382  1453 15  5  0 80
 0  1    160 502340   1252 301096    0    0  3332     0 1358  1624  7  5  0 88
 0  1    160 495236   1260 308216    0    0  3588     0 1323  1631  2  3  0 95
 1  1    160 487620   1268 315640    0    0  3716     0 1355  1175  7  2  0 91
 0  2    160 480708   1276 322120    0    0  3204 16732 1423  1354  2  5  0 93

You can see text version here (in case this got wrapped):

http://www.vanja.com/vmstat.txt

I've tried vmstat on my machine, with IDE disks, and I've noticed that I 
ave much less 'cs' (context switches), although it might be because I'm
not having as many processes in the background (problematic computer
is running KDE :).

On my computer, number of blocks in (bi) gets into tens of thousands,
while problematic computer has 1500-3000 bs/second.

Does anyone know what I might do in order to find what the problem
might be?

I couldn't find any SATA specific tools, which might help with
troubleshooting. hdparm -tT tests show:

/dev/sda:
 Timing cached reads:   2408 MB in  2.00 seconds = 1202.98 MB/sec
 Timing buffered disk reads:  150 MB in  3.02 seconds =  49.61 MB/sec

/dev/sdb:
 Timing cached reads:   2628 MB in  2.00 seconds = 1313.54 MB/sec
 Timing buffered disk reads:  166 MB in  3.02 seconds =  54.88 MB/sec

All filesystems are ext3.

This "problematic" computer has nforce3 motherboard, I have nforce2.
Same CentOS, but no SATA on my computer.

This really affects complete performance of computer, and any help or
ideas are welcome.

Btw, no problems with transfer under Windows :(

Thanks.

Vanja



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