To make sure we have a very stable benchmark, the same machine, without any changes other than switching AHCI on through the BIOS was tested twice. Granted, this is an older motherboard in a machine used for testing and development, the results on other motherboards should be similar.

The difference in the input/output and seeks are negligible. The sequential create and delete results generally show much improved results for create/delete but the read results are virtually unchanged. This is probably a result of the Native Command Queuing (NCQ) enabled in AHCI that isn’t present in the piix driver. Since the firmware on the disk can reorder requests based on the rotational position of the data it needs to access, there are some benefits.

Since it doesn’t appear to be detrimental to enable AHCI, and it does increase performance of two particular portions of the benchmark that may not really be exercised in a normal webserver environment, if you have the ability to run your hardware in AHCI mode rather than the native piix mode, I would suggest using AHCI.

The command line used: /usr/sbin/bonnie -n 384

piix results:

Version  1.96       ------Sequential Output------ --Sequential Input- --Random-
Concurrency   1     -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
kvm              4G   439  99 52686  15 27168   5  2039  99 62782   4 228.9   3
Latency             48125us    1645ms    1545ms   16144us     137ms     863ms
Version  1.96       ------Sequential Create------ --------Random Create--------
kvm                 -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
              files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP
                384 17299  43 379058  99   777   1 24781  49 522877 100   579   1
Latency              1773ms     169us   18519ms    1403ms      14us   14935ms
1.96,1.96,kvm,1,1252886317,4G,,439,99,52686,15,27168,5,2039,99,62782,4,228.9,3,384,,,,,17299,43,379058,99,777,1,24781,49,522877,100,579,1,48125us,1645ms,1545ms,16144us,137ms,863ms,1773ms,169us,18519ms,1403ms,14us,14935ms

AHCI results:

Version  1.96       ------Sequential Output------ --Sequential Input- --Random-
Concurrency   1     -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
kvm              4G   430  98 52639  14 27533   5  2066  99 62991   4 224.5   1
Latency             50870us    1532ms    1655ms   10203us   21423us     953ms
Version  1.96       ------Sequential Create------ --------Random Create--------
kvm                 -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
              files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP
                384 28173  56 373407  98  1645   2 31110  61 522376  99  1026   1
Latency              1363ms     157us   12877ms    1216ms      61us   11397ms
1.96,1.96,kvm,1,1252887577,4G,,430,98,52639,14,27533,5,2066,99,62991,4,224.5,1,384,,,,,28173,56,373407,98,1645,2,31110,61,522376,99,1026,1,50870us,1532ms,1655ms,10203us,21423us,953ms,1363ms,157us,12877ms,1216ms,61us,11397ms

Output from lspci -vvnn with the piix driver selected:

00:1f.2 IDE interface [0101]: Intel Corporation 82801H (ICH8 Family) 4 port SATA IDE Controller [8086:2820] (rev 02) (prog-if 8a [Master SecP PriP])
	Subsystem: Super Micro Computer Inc Device [15d9:8780]
	Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
	Status: Cap+ 66MHz+ UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- SERR-

Output from lspci -vvnn with the ahci driver selected:
00:1f.2 SATA controller [0106]: Intel Corporation 82801HB (ICH8) 4 port SATA AHCI Controller [8086:2824] (rev 02) (prog-if 01 [AHCI 1.0])
	Subsystem: Super Micro Computer Inc Device [15d9:8780]
	Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx+
	Status: Cap+ 66MHz+ UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- SERR-

	Kernel driver in use: ahci

Technical Specs:
Debian/Squeeze/Sid (Testing)

Supermicro P4SBE Motherboard

Intel(R) Core(TM)2 CPU          6300  @ 1.86GHz