Pillar Axiom 600 Storage System
 
Pillar Axiom 300 Storage System
 
Pillar Axiom 500 Storage System
 

PLA-Support>Sun Systems>DISK>Axiom>SN-DK: Ax600
 

Settings for throttling queue depth in VMWare ESX/ESXi

In this Document

Symptoms

Changes

Cause

Solution

References

Created from <SR 3-7823472850>

Applies to:

Symptoms

If QFULL conditions exist, the ESX VMkernel log may contain entries similar to:

• In ESX 3.x
  • status = 40/0 0x## 0x## 0x##
• In ESX/ESXi 4.0 and later:
  • H:0x0 D:0x28 P:0x0 Valid sense data: 0x## 0x## 0x##
  • H:0x0 D:0x08 P:0x0 Valid sense data: 0x## 0x## 0x##

The hexadecimal 28 or decimal 40 in the error is the SCSI status code for the queue full state. The value 0x08 in the above error is the SCSI Status code indicating a device busy state.

Changes

None.

Cause

 IO is heavier than queue depth allows.

Solution

VMware ESX 3.5 Update 4 introduces an adaptive queue depth algorithm that adjusts the LUN queue depth in the VMkernel I/O stack. This algorithm is activated when the storage array indicates I/O congestion by returning a BUSY or QUEUE FULL status. These status codes may indicate congestion at the LUN level or at the port (or ports) on the array. When congestion is detected, VMkernel throttles the LUN queue depth. The VMkernel attempts to gradually restore the queue depth when congestion conditions subside.

This algorithm can be activated by changing the values of the QFullSampleSize and QFullThreshold parameters. When the number of QUEUE FULL or BUSY conditions reaches the QFullSampleSize value, the LUN queue depth reduces to half of the original value. When the number of good status conditions received reaches the QFullThreshold value, the LUN queue depth increases one at a time.

QFullSampleSize to a value greater than zero. The usable range is 0 to 64.  For Pillar Axiom arrays the recommended value would be 32.

QFullThreshold to a value lesser than or equal to QFullSampleSize. The usable range is 1 to 16.  For Pillar Axiom arrays the recommended value is  to  set the QFullThreshold value to 4.

References

This solution has no attachment