Operating System - OpenVMS
Showing results for 
Search instead for 
Did you mean: 

OpenVMS 8.3 SSH performance

Rikki hinn Ogurlegi
Frequent Advisor

OpenVMS 8.3 SSH performance

Hello all,


I have a two node VMS cluster running OpenVMS 8.3.  These two nodes run a X11 graphical program many people here need to access.  Clients are mostly using Xming (or hummingbird) on Windows.

Traditionally people have logged in via telnet, set their DISPLAY variable and then run the program.   This is however quite fragile as IP addresses can change and the telnet service on the VMS boxes seems to stop working rather frequently.

So I started experimenting with using SSH and SSH X forwarding to handle this for me, and as an added bonus get rid of plain text passwords and other data flowing thru the LAN here.

Both Xming and Hummingbird know how to use either putty.exe or plink.exe so the setup and config was easy.  However once the app is running I see almost a 10 fold increase in latency when using the program.   Flipping pages in the app was quite responsive when X was connecting directly but becomes very sluggish via SSH.

I tested logging in to a Linux machine that is in the same server room as the VMS cluster with putty and X11 forwarding and running apps on them and they did not show any slowness over SSH, compared to direct X11 connections.


So I need to figure out why SSH connections to OpenVMS 8.3 are so slow.   It does remind me of a very old problem I had with HP-UX back in the day when HP-UX did not have a decent /dev/random device and SSH was starved for decent entropy for encryption purposes, but I have no way to know if this is the case on VMS as I'm really not that good with VMS.


Any help would be appreciated.

Thanks in advance,



Steven Schweda
Honored Contributor

Re: OpenVMS 8.3 SSH performance

Rikki hinn Ogurlegi
Frequent Advisor

Re: OpenVMS 8.3 SSH performance

>> I have a two node VMS cluster running OpenVMS 8.3.  [...]
>   Not much meat on that bone.  About what kind of hardware are we
> talking?  AlphaStation 200/100?  Some fancy multi-GHz-CPU server?
> Memory?  Quotas?

ELAS_SYS:ISLANDV2.0==>sh cpu
System: ELAS05, AlphaServer DS15A
CPU ownership sets:
   Active               0
   Configure            0
CPU state sets:
   Potential            0
   Autostart            0
   Powered Down         None
   Not Present          None
   Hard Excluded        None
   Failover             None
ELAS_SYS:ISLANDV2.0==>sh mem
              System Memory Resources on  9-JAN-2013 11:23:03.97
Physical Memory Usage (pages):     Total        Free      In Use    Modified
  Main Memory (512.00MB)           65536       16090       48610         836
Extended File Cache  (Time of last reset: 15-JUL-2012 05:45:12.01)
Allocated (MBytes)            111.62    Maximum size (MBytes)           256.00
Free (MBytes)                   0.00    Minimum size (MBytes)             3.12
In use (MBytes)               111.62    Percentage Read I/Os                79%
Read hit rate                     91%   Write hit rate                       0%
Read I/O count            4072288894    Write I/O count             1034334960
Read hit count            3741138370    Write hit count                      0
Reads bypassing cache          75807    Writes bypassing cache           31882
Files cached open                490    Files cached closed                147
Vols in Full XFC mode              0    Vols in VIOC Compatible mode         3
Vols in No Caching mode            0    Vols in Perm. No Caching mode        0
Granularity Hint Regions (pages):   Total        Free      In Use    Released
  Execlet code region                1024           0         980          44
  Execlet data region                 512           0         414          98
  S0S1 Executive data region          680           0         680           0
  S0S1 Resident image code region    2048           0        1213         835
Slot Usage (slots):                Total        Free    Resident     Swapped
  Process Entry Slots                356         292          62           2
  Balance Set Slots                  354         292          60           2
Dynamic Memory Usage:              Total        Free      In Use     Largest
  Nonpaged Dynamic Memory (MB)     15.45       10.26        5.18        0.15
  Bus Addressable Memory  (byt      0.00        0.00        0.00        0.00
  Paged Dynamic Memory    (MB)      3.62        2.05        1.57        2.03
  Lock Manager Dyn Memory (MB)      2.57        1.11        1.45
Buffer Object Usage (pages):                  In Use        Peak
  32-bit System Space Windows (S0/S1)              2          34
  64-bit System Space Windows (S2)                 0           0
  Physical pages locked by buffer objects          2          34
Memory Reservations (pages):       Group    Reserved      In Use        Type
  Total (0 bytes reserved)                         0           0
Swap File Usage (8KB pages):                   Index        Free        Size
                                                   1        2640        2768
Paging File Usage (8KB pages):                 Index        Free        Size
                                                 254       45980       66048
  Total committed paging file usage:                                   46129
Of the physical pages in use, 6818 pages are permanently allocated to OpenVMS.
Not sure how to see if quotas are getting in the way of SSH processing.
>> [...] the telnet service on the VMS boxes seems to stop working rather
>> frequently.
>  Not a very complete problem description.

It's the best I can do. I have'nt diagnosed that problem as I still feel that ssh is the way to go.
>> [...] very sluggish [...]
> What investigation have you done?  Is the CPU (are all the CPUs)
> busy while this stuff is running?  Memory?  Page-fault rate?  For a
> start:

Just basic things as I'm not that familiar with VMS.    The X11 program we are running displays pages that contains multiple text fields and some graphs. The most telling of these tests is to simply open the program and quickly hit page down a few times.  When using direct X connections the program flashes as many pages as the page down key was hit.
But when using X forwarding via ssh, the program just prints the first page and then the last.   It may print a few pages inbetween if the page down key is pressed often enough.
It also takes longer to start and do most other operations.
>> [...] a Linux machine [...]
> The description of this hardware is no more useful than the earlier
> one of the VMS hardware.  I would not be amazed if a modern,
> resource-rich x86 system were faster than some decade-old, resource-poor
> Alpha system.  But, with my weak psychic powers, I know approximately
> nothing about your hardware (or the users' resource quotas, or anything
> else, really).

The machine is just a single cpu DL360 G5 box running RHEL6.  Im pretty sure I did not describe my problem well enough but in my mind, running SSH should not be that much of a hassle for any machine.  I've got 15 year old HP9000 L2000 machines with PA-RISC cpu's running HP-UX 11.23 who perform very well with SSH.
Steven Schweda
Honored Contributor

Re: OpenVMS 8.3 SSH performance

Respected Contributor

Re: OpenVMS 8.3 SSH performance

Slot Usage (slots): Total Free Resident Swapped
Process Entry Slots 356 292 62 2
Balance Set Slots 354 292 60 2


The portion of the SHO MEM above indicates to me that you are running a bit short on memory. As indicated by Steven, get more memory for this system. That should make a tremendous difference overall.