Block size related errors on hardware with Emulex cards

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Environment

SUSE Linux Enterprise Server 11 Service Pack 1 (SLES 11 SP1)
SUSE Linux Enterprise Server 11 Service Pack 2 (SLES 11 SP2)
SUSE Linux Enterprise Server 11 Service Pack 3 (SLES 11 SP3)

Situation

On SLES11 SP1, SP2 and SP3, when trying to use Symantec backup software with the previously used block size of 512k an error was observed:-

Cannot read: Device or resource busy

This could be duplicated easily using 'tar' with the parameter '-b 1024' (which equals a block size of 512k).

Resolution

The problem was identified as occurring due to an interaction between the 'st' tape driver and the Emulex 'lpfc' driver.

In later versions of the Emulex driver, a parameter, 'lpfc_sg_seg_cnt' is exposed and by default is set 'too low'.

By changing this value from the default of 64, to a value of 128 or 256, the issue with 512k block sizes is resolved.

On SLES11 SP3, this is accomplished by the following steps:-

Create a file /etc/modprobe.d/lpfc.conf and add to this file:
options lpfc lpfc_sg_seg_cnt=256

Run 'mkinitrd' to generate a new initrd that will include this lpfc parameter change.

Reboot the server.

To view the current setting of the lpfc_sg_seg_cnt parameter use the command 'systool -v -m lpfc'.

Cause

Emulex lpfc_sg_seg_cnt parameter set too low.

Additional Information

There are suggestions that increasing the value of the 'lpfc_sg_seg_cnt' parameter may also provide a noticeable performance increase in the throughput of the Emulex cards.

This problem is not known to occur on SLES11 with no service pack.

Disclaimer

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