topic Re: VMS 8.3 Data compression in Operating System - OpenVMS

VMS 8.3 Data compression

Michael Menge — Mon, 23 Oct 2006 08:16:03 GMT

With VMS 8.3 data compression can be enabled for cluster interconnects. How can I verify that a connection is using this? I haven't found any show-command in $MC LANCP or $MC SCACP giving this information.

Re: VMS 8.3 Data compression

Volker Halle — Mon, 23 Oct 2006 08:46:23 GMT

Michael,

SCACP> SHOW VC/SDA remote-node

seems to show, whether VC compression has been requested for the virtual circuit and if compression is active:

- VC Characteristics ---
...
Options 4 = compression active

- VC Mgt Settings ---
...
VC Options 4 = compression requested

You can test this, by requesting compression on a VC to a node, which does NOT (yet) supported compression. A VC which supports compression is the VC to the local (V8.3) node:

SCACP> SET VC/COMPRESSION

Volker.

Re: VMS 8.3 Data compression

Michael Menge — Tue, 24 Oct 2006 03:45:29 GMT

Volker,

I had set NISCS_PORT_SERV=16 (Bit4 = 1) to request data compression. It seems this was not enough.
SCACP> SHOW VC/SDA remote-node
shows:
VC Characteristics: Options 10 (10=?)
VC Mgt Settings: VC Options 0
After
SCACP> SET VC/COMPRESSION node
the values are
VC Characteristics: Options 14
VC Mgt Settings: VC Options 4

So what exactly is to do to enable compression between two nodes (nod1,nod2) from boot-time on?
In System Management Utilities Reference Manual you can read about NISCS_PORT_SERV:
page D-39:
Setting bits 0 and 1 (decimal value 3) enables data checking
Setting bit 4 enables data compression (what about bit 2 and 3?)
page 5-18:
The /NOCOMPRESSION qualifier does not override compression enabled by setting bit 2 of NISCS_PORT_SERV.

Bit 2 is decimal 4. Is there a mismatch in the doku between bit 4 and decimal value 4 (bit 2)?

Re: VMS 8.3 Data compression

Volker Halle — Wed, 25 Oct 2006 00:32:41 GMT

Michael,

assuming that SCACP> SET VC/COMPRESSION knows what it's doing, bit 2 (hex bitmask value 4) seems to control VC compression.

The help text in SYSGEN> HELP SYS_P NISCS_PORT_SERV is therefore probably wrong, as well as parts of the documentation.

Set NISCS_PORT_SERV=4 if you want VC compression enabled at boot time.

If you can, please log a call with HP to fix the documentation and help text for the future.

Volker.

Re: VMS 8.3 Data compression

Michael Menge — Wed, 25 Oct 2006 06:52:07 GMT

I have logged a call with HP.

Re: VMS 8.3 Data compression

Volker Halle — Fri, 27 Oct 2006 02:31:53 GMT

Michael,

I've found the following in the OpenVMS Bootcamp 2006 presentation 'V8.3 Cluster Interconnect New Features':

Data Compression: Enabled on a per VC basis, or globally for all VCs by using:

- SCACP> SET VC nodename /COMPRESS
- NISCS_PORT_SERV bit 2 (mask: 4 hex) for all VCs
- Availability Manager fix command is coming.

This should settle the discussion.

Volker.