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SubjectRe: iozone lies/bug ?
J.A. Magallón wrote:
> Hi all...
>
> This is a curious thing, I think...
> I wanted to test the speed of an usb stick, and as a first step used hdparm
> on my root disk (real SCSI) and on the stick:
>
> werewolf:/media/media# lsscsi
> [1:0:0:0] disk SEAGATE ST336807LW 0C01 /dev/sda
> [1:0:1:0] disk SEAGATE ST336807LW 0C01 /dev/sdb
> [2:0:0:0] disk ATA ST3120022A 3.06 /dev/sdc
> [2:0:1:0] cd/dvd HL-DT-ST DVDRAM GSA-H10N JL12 /dev/sr0
> [4:0:0:0] disk ATA ST3200822AS 3.01 /dev/sdd
> [5:0:0:0] disk ATA WDC WD3200AVJS-6 12.0 /dev/sde
> [7:0:0:0] disk USB DISK 2.0 1219 /dev/sdf
> werewolf:/media/media# hdparm -tT /dev/sda /dev/sdf
>
> /dev/sda:
> Timing cached reads: 1402 MB in 2.00 seconds = 700.54 MB/sec
> Timing buffered disk reads: 226 MB in 3.02 seconds = 74.86 MB/sec
>
> /dev/sdf:
> Timing cached reads: 1272 MB in 2.00 seconds = 635.69 MB/sec
> Timing buffered disk reads: 52 MB in 3.02 seconds = 17.20 MB/sec
>
> Well, looks reasonable.
> But, as hdparm is not a 'serious' test, and I wanted also write speed,
> used iozone:
>
> werewolf:/media/media# iozone -v
> 'Iozone' Filesystem Benchmark Program
>
> Version $Revision: 3.287 $
> Compiled for 32 bit mode.
>
> But it gives strange results:
>
> for sda1 (/):
>
> Machine = Linux werewolf.home 2.6.26-jam07 #1 SMP PREEMPT Mon Sep 1 01:47:23 C Auto Mode
> Auto Mode
> File size set to 4096 KB
> Command line used: iozone -M -a -s 4m
> Output is in Kbytes/sec
> Time Resolution = 0.000001 seconds.
> Processor cache size set to 1024 Kbytes.
> Processor cache line size set to 32 bytes.
> File stride size set to 17 * record size.
> random random bkwd record stride
> KB reclen write rewrite read reread read write read rewrite read fwrite frewrite fread freread
> 4096 4 180855 742576 1275252 1130840 1143176 597607 998780 670266 1168616 231962 670815 1071129 1259145
> 4096 8 247673 809183 1246875 1407083 1351815 711728 1176673 854936 1298668 236817 744321 1233363 1519851
> 4096 16 251644 851010 1123131 1691931 1668431 716459 1094017 931544 1259145 245622 793337 1110328 1659643
> 4096 32 253245 871663 1463432 1764719 1808388 757396 1339875 885813 1393197 261107 796112 1128374 1742978
> 4096 64 254837 862332 1139037 1789405 1585752 779448 1136199 961728 1844214 259684 799687 1124965 1538114
> 4096 128 250090 868154 1177029 1715966 1700996 771810 1181084 980842 1643659 228405 792569 1003429 1720285
> 4096 256 242984 791959 950372 718080 930274 826472 694472 708038 913470 223751 566606 698737 918385
> 4096 512 238696 664406 764459 803304 720492 519335 727660 420102 686557 212735 416768 728695 695534
> 4096 1024 232926 667198 711975 773266 735896 689562 781828 663857 742297 253183 541297 658732 816912
> 4096 2048 243548 659167 653899 738807 728048 632684 638304 493137 599707 305011 660858 664180 792569
> 4096 4096 218417 655142 857449 732729 694826 696717 689098 557278 627643 242913 610705 713588 784073
>
> for sdf1:
>
> Machine = Linux werewolf.home 2.6.26-jam07 #1 SMP PREEMPT Mon Sep 1 01:47:23 C Auto Mode
> Auto Mode
> File size set to 4096 KB
> Command line used: iozone -M -a -s 4m
> Output is in Kbytes/sec
> Time Resolution = 0.000001 seconds.
> Processor cache size set to 1024 Kbytes.
> Processor cache line size set to 32 bytes.
> File stride size set to 17 * record size.
> random random bkwd record stride
> KB reclen write rewrite read reread read write read rewrite read fwrite frewrite fread freread
> 4096 4 391850 843302 885058 1159992 746900 704385 778707 566371 941825 481712 772247 1204705 795494
> 4096 8 385690 981087 1036709 1419270 945740 755162 978967 555842 1211475 390392 919622 1209329 1071970
> 4096 16 613438 1121897 1335497 1594434 1441745 683008 1217598 973152 1117903 558038 1014363 1144453 1552103
> 4096 32 559635 968335 1494912 1601847 1676627 1129619 1491081 1264978 1675941 604932 1051334 1217598 1629276
> 4096 64 627925 1197687 1557477 1697406 1573569 1082738 1589445 1237462 1755679 587830 1090812 1216513 1678000
> 4096 128 538446 1177653 1366266 1268879 963537 796422 981548 983197 1582077 428272 977099 1431167 1643000
> 4096 256 611078 1160652 907177 1041725 1114861 1214349 1088204 1161985 813343 454051 552021 919003 984852
> 4096 512 448633 912842 725981 782419 722526 983197 579103 870748 644937 432341 632684 718092 768336
> 4096 1024 473859 816750 717209 795504 738683 660964 694472 793337 716083 385070 699573 718092 760207
> 4096 2048 513161 789051 685059 768041 718974 652437 643418 639500 715583 486749 881049 715708 747854
> 4096 4096 505174 700760 835748 775173 786029 794414 797507 718470 594830 408904 835066 637608 670815
>
> First, Output is not in Kb, or I have a disk that gives 1Gb/s... :).
> And second, how can both drives give the same ? The file is too small ?
> Do I need -e to iozone to account for sync ? But that would not affect read
> speed...
> Strange (for my understanding).

A file size of 4096KB is probably just running entirely out of the cache..
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