Re: Backup save set compression


"Jur van der Burg" <"lddriver at digiater dot nl"> wrote in message
news:46c1e7ff$0$241$e4fe514c@xxxxxxxxxxxxxxxxx
What's wrong here?

There's probably a record of less than 14 bytes in lenght in the file,
and the VMS i/o subsystems rejects that for tapes. And yes, that's
documented.

Talking about data compression, there's a big gotcha when you use it.

If you create a compressed saveset on disk, and copy it to another system
with ftp (binary copy), and copy it back you can't restore it. The records
for a compressed saveset are now variable length, and ftp has a problem
with
that in binary mode. And if you use text mode you will get a problem for
sure. Also, after restoring, backup/repair does not know how to handle
compressed savesets.

I ended up doing a 'set file/attr=(rfm=fix,rat=none,mrs=512,lrl=512)' on
the saveset before copying, and a 'set
file/attr=(rfm=var,rat=none,mrs=32256,lrl=32256)'
when I want to restore it.


Jur - That's documented in my utilities presentation.



I found this out when testing backup procedures. You see, anyone can
create a
backup, but restoring is another art. Testing if you can reaaly restore it
may pay off!

Jur.


Scott Greig wrote:
"Guy Peleg" <guy.peleg@xxxxxxxxxxxxxxxxxxxxx> wrote in message
news:46c17fb5$0$16340$88260bb3@xxxxxxxxxxxxxxxxxxxx
"Scott Greig" <jsgreig@xxxxxxxxxxx> wrote in message
news:f9pru1$2gei$1@xxxxxxxxxxxxxxxxx
Hello all:

The Alpha 8.3 patch site lists a new Backup patch
(VMS83A_BACKUP-V0300) that describes a fix
for a problem concerning the use of the /Journal
switch and the /Data_Format=Compressed switch.

The /Data_Format switch???!!!???
This is a mistake. /DATA_FORMAT=COMPRESS should not have been
documented. It is very reliable, and as mentioned by Ian, it uses
ZLIB as the compression engine. It has one major limitation, it can
only compress savesets when writing to disks. Writing compressed
savesets
to Tapes is not supported.

Further to this - it seems that I cannot even $ COPY the saveset
to a tape - I get

$ dir/fu sys$sysdevice:[000000]qq.bck
Directory SYS$SYSDEVICE:[000000]
QQ.BCK;1 File ID: (6180,230,0)
Size: 8364/8365 Owner: [1,1]
Created: 14-AUG-2007 11:18:28.79
Revised: 14-AUG-2007 11:18:37.99 (1)
Expires: <None specified>
Backup: <No backup recorded>
Effective: <None specified>
Recording: <None specified>
Accessed: <None specified>
Attributes: <None specified>
Modified: <None specified>
Linkcount: 1
File organization: Sequential
Shelved state: Online
Caching attribute: No_caching
File attributes: Allocation: 8365, Extend: 0, Global buffer count: 0
No version limit
Record format: Variable length, maximum 32256 bytes, longest 32256 bytes
Record attributes: None
RMS attributes: None
Journaling enabled: None
File protection: System:RWED, Owner:RWED, Group:, World:
Access Cntrl List: None
Client attributes: None
Total of 1 file, 8364/8365 blocks.
$ init mka600: save/media=compact
$ mount mka600: save/media=compact
%MOUNT-I-MOUNTED, SAVE mounted on _GEMAXP$MKA600:
$ copy sys$sysdevice:[000000]qq.bck mka600:/log
%COPY-E-OPENOUT, error opening MKA600:[SCOTT.CLIENTS.DND]QQ.BCK;1 as
output
-RMS-E-CRE, ACP file create failed
-SYSTEM-F-BADATTRIB, bad attribute control list
%COPY-W-NOTCOPIED, SYS$SYSDEVICE:[000000]QQ.BCK;1 not copied

What's wrong here?

Scott

.... and AFAIK, VMS engineering use it.
So, I tried it out - and achieved a 67% compression
rate for the output save set (138087 blocks with
compression, 412461 blocks without.)

HELP BACKUP does not mention this switch.

My question - when was this implemented, and
how reliable is the output save set?
Introduced with OpenVMS V8.3. It's an undocumented
feature....use it at your own risk.

Cheers,
Scott





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