dmraid FakeRAID vs Linux Software RAID
With so many motherboard and PCI RAID devices being sold cheaply to the techie consumer it has to be noted that 99% of them are infact Fake RAID.
Ask yourself why buy a RAID card that costs £300+ when my cheap £30 motherboard has built in RAID ! Ask yourself indeed the difference between FakeRAID and real RAID ;)
Here are some performance benchmarks comparing FakeRAID vs Linux Software RAID…
Hardware
Setup A : dmraid FakeRAID
PCI Silicon Image 3512 RAID Controller.
00:0c.0 RAID bus controller: Silicon Image, Inc. SiI 3512 [SATALink/SATARaid] Serial ATA Controller (rev 01)
2 x Maxtor 6V160E0 Rev: VA13 SATA disks. (160gb each)
root@ultra:~# df -k
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/mapper/sil_agbheaaedgdc1 304397776 8813680 280121536 4% /
Setup B : Linux Software RAID
VT8237A SATA onboard controller with RAID off
00:0f.0 IDE interface: VIA Technologies, Inc. VT8237A SATA 2-Port Controller (rev 80)
2 x SAMSUNG HD160JJ Rev: ZM10 SATA disks. (160gb each)
root@ultra:~# df -k
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/md0 303765224 1848008 286486800 1% /
Benchmark Results
hdparm
dmraid [ 102.89 MB/sec ]
root@ultra:~# hdparm -tT /dev/mapper/sil_agbheaaedgdc1
/dev/mapper/sil_agbheaaedgdc1:
Timing cached reads: 3248 MB in 2.00 seconds = 1623.42 MB/sec
Timing buffered disk reads: 310 MB in 3.01 seconds = 102.89 MB/sec
Software RAID [ 118.28 MB/sec ]
root@ultra:~# hdparm -tT /dev/md0
/dev/md0:
Timing cached reads: 3284 MB in 2.00 seconds = 1642.35 MB/sec
Timing buffered disk reads: 356 MB in 3.01 seconds = 118.28 MB/sec
bonnie
dmraid [ 92204 K/sec ]
shaf@ultra:~$ bonnie
Version 1.03Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP
ultra 2G 38388 97 92204 31 34184 11 30460 69 84613 16 167.4 0
Software RAID [ 114909 K/sec ]
shaf@ultra:~$ bonnie
Version 1.03Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP
ultra 2G 50805 97 114909 29 40225 9 45872 82 99841 13 245.6 0
bootchart
dmraid [ 33 seconds to boot ] (Click to enlarge)
Software RAID [ 20 seconds to boot ] (Click to enlarge)
Conclusion
Although the bootchart results are somewhat skewed I would still have to say unequivocally that Linux Software RAID has grabbed my attention over FRAID.