Knowledge Base

Storage PortFan-in Ratio

This is defined as the number of initiators sharing the same Storage Processor Port.

Consult with HDS support about how to identify and the best practice for the Fan-in Ratio.

VMware recommends reducing the Fan-in Ratio if you encounter SCSI Reservation Failures.

LUN Type

• VMware recommends using non-LUSE based LUNs for VMFS volumes.
• If you are using LUSE based LUNs, make sure that the Microcode version on the array is at least 50-07-66-00/00 then enable Host Mode Option 19. For more information, see VMotion failure of virtual machines located on LUSE LUNs on HDS TagmaStore USP/NSC Arrays (3408142). This applies to Virtual LUNs as well.
• On USP V and USP virtual machines, set the Host Mode to "VMware" 

Queue depth, LUN-to-ESX ratio, LUN-to-VM ratio 

Based on log and Fibre Channel trace analysis, one cause of this issue is that the Command Queue is exhausted.

• Reduce the Queue Depth on each Server's HBA connected to that array.
• Reduce the number of ESX Server hosts sharing a given LUN or set of LUNs on that array.
• Reduce the number of VMs per LUN so that the possible number of hosts accessing a given LUN would be reduced. For example, if you limit the number of virtual machines per LUN to 4, the highest number of ESX hosts running these virtual machines does not exceed 4 in a DRS/HA cluster. 
  
  Note: This option may result in using more LUNs of smaller sizes. The maximum number of LUNs accessible by a ESX 3.x and ESX 4.x is 256.

Recommended the Queue Depth setting on the HBA

 Number of hosts sharing a LUN         Queue Depth Value

 8                                                         2

 4                                                         4

 2                                                         8

As fewer hosts share a given LUN, the queue depth setting is higher.

Note:VMware has not received similar reports for USP-V or USP-VM and the above does not apply to these models. The HBA driver’s default queue depth is sufficient.

Changing the Queue Depth

QLogic HBAs:  

1. Run the following command to identify the HBAs driver name:
   
   # vmkload_mod -l | grep qla
   
   The output appears similar to:
   
   qla2300_707_vmw
   
   
2. Substitute the <driver_name> parameter below with the name from the above output. Substitute the nn parameter with the Queue depth value calculated above, and run the following commands:
   
   # esxcfg-module -s "ql2xmaxqdepth=nn" <driver_name>
   # esxcfg-boot -b
   # reboot

Emulex HBAs:

1. Run the following command to identify the HBAs driver name:
   
   # vmkload_mod -l | grep lpfcdd
   
   The output appears similar to:
   
   lpfcdd_7xx
   
   
2. Substitute the <driver_name> parameter below with the name from the above output. Substitute the nn parameter with the Queue depth value calculated above.
   
   # esxcfg-module -s “lpfc0_lun_queue_depth=nn” <driver_name>
   
   If you have 2 Emulex HBAs in the server, the command is:
   
   # esxcfg-module -s "lpfc0_lun_queue_depth=nn lpfc1_lun_queue_depth=nn" <driver_name>
   # esxcfg-boot -b
   # reboot

• Virtual LUNs must match the physical LUNs RAID Level. For example, if the physical LUN is RAID5, the virtual LUN must be setup using RAID5 as well.
• A physical LUN that is represented by a Virtual LUN must be on Tier 1 type physical disks (Fibre SCSI Disks or Fibre SAS Disks) and with minimum 10K RPM rating, to provide the best I/O performance.
• LUSE LUNs should not be used with Virtual LUNs. For more information, see http://www.vmware.com/pdf/hds_svd_technote.pdf.