Request clear explaination of the st_ats_enable parameter

[Paul Frets]

I am looking for a cut-and-dried explaination of the st_ats_enable kernel parameter and when it is needed in a shared storage (SSO) environment.

I've installed SANs in two HP shops now. The first one was in January. It required several PHCO and PHKL patches, and st_ats_enable=0 on all attached hosts, before the hosts would quit doing a scsi lock on the the tape drives in our SSO environment. I only figured this out after hours of time on the HP support site, where I found the explaination of st_ats_enable to be poorly documented.

I just returned from another install, where my customer had the latest patches installed but had not yet set st_ats_enable=0. My client has been running for some time now WITHOUT the st_ats_enable set to zero, in a shared storage environment, and has no scsi locking problems.

[Michael Tully]

Hi Paul,

I wish I could explain it too.... I also have a SAN which has *had* various problems over a six month period. We were also advised to change the "st_ats_enabled" parameter. I have not seen any differences in the way ours works N4000 & L2000 --> Brocade switch running fabric --> 20/700 HP Tape library. We were also advised to load a number of patches and make changes to our EMS config. In regards to the kernel parameter itself the only information I can find on my HPUX box, the description says "unknown"... as for the Hp site I have found nothing... although I will ask them myself... WIll post the answer if I get one.

Cheers
Michael

[Oliver Haensel]

Hi Paul,

The static kernel tunable parameter st_ats_enable was originally designed for ATS services (Advanced Tape Services) with MC Service Guard. When this parameter is enabled an implicit SCSI reserve and release is performed during the open and close sequence in the tape driver. You can also use ATS to clean up reservations from a second host. This could interfere the reservations made by a backup server and therefore bring the backup to fail. That's why ATS should not be configured for SAN configurations.

-Oliver-

[Sanjay_6]

Hi Paul,

The Kernel Parameter st_ats_enabled was added thru patch PHKL_20062 in 10.20.

Listed below is the latest patch in that category. The explanation for patch PHKL_20062 is also documented as well as the purpose of st_ats_enabled parameter.

http://us-support.external.hp.com/cki/bin/doc.pl/sid=18c2db481bb9f440e2/screen=ckiDisplayDocument?docId=200000055334283

Hope this helps.

thanks

[Sanjay_6]

Hi Paul,

It's me again. Just checked the patches for UX 11.0 . The patch for 11.0 for st_ats_enabled is PHKL_19805, the latest patch in this series is PHKL_23790. Follow the thread below for more information.

http://us-support.external.hp.com/wpsl/bin/doc.pl/screen=wpslDisplayPatch/sid=fe740a3301299a9f9d?PATCH_PATH=/hp-ux_patches/s700_800/11.X/PHKL_23790&HW=s800&OS=11.00

Hope this helps.

thanks