kern/114438: Anomalous performance with multiple arrays and amr(4)

[Thomas Hurst]

>Number:         114438
>Category:       kern
>Synopsis:       Anomalous performance with multiple arrays and amr(4)
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Mon Jul 09 12:40:04 GMT 2007
>Closed-Date:
>Last-Modified:
>Originator:     Thomas Hurst
>Release:        FreeBSD 6.2-STABLE amd64
>Organization:
>Environment:
System: FreeBSD voi.nightsdawn.sf 6.2-STABLE FreeBSD 6.2-STABLE #0: Wed Jul 4 13:46:52 BST 2007 root at voi.nightsdawn.sf:/usr/obj/usr/src/sys/VOI amd64

	8GB dual dual core Opteron

	amr0: <LSILogic LSI MegaRAID SATA300-8X PCI-X> Firmware 814B, BIOS H431, 128MB RAM
	amrd0: 190713MB (390580224 sectors) RAID 1 (optimal)
	amrd1: 381485MB (781281280 sectors) RAID 1 (optimal)
	amrd2: 381485MB (781281280 sectors) RAID 1 (optimal)
>Description:
	Performing heavy random IO on any one array causes other arrays to
	stall intermitently.  For example:

	find /usr >/dev/null & # on amrd0
	dd if=/dev/amrd1 of=/dev/null bs=128k

	gstat shows amrd0 doing a few hundred ops/sec and up to a few MB/s
	amrd1 runs at the expected 65MB/s for ~10 seconds, then stops for 2-3,
	before returning to 65MB/s.

	This behavior is seen with lighter serial transfers; I normally notice it
	while streaming movies or music at 100-1000k/s and daily run kicks in,
	causing annoying pauses in playback without the use of fairly large buffers.

	Multiple serial transfers on different arrays do not have the same problem;
	I can dd from or to all arrays without unexplained pauses.

	ata(4) disks on the system are unaffected.
>How-To-Repeat:
	See above.
>Fix:

	


>Release-Note:
>Audit-Trail:
>Unformatted: