[Supplementary] is vdump compressing data even when I don't ask it to?

From: speakmaj@mskcc.org
Date: Thu Nov 21 2002 - 11:59:56 EST

• Next message: Kevin Beauchamp: "Problems adding DLT to AlphaServer 1000A"
• Previous message: Brehl, Blake: "SUMMARY: print leading or trailing lines in grep"
• Messages sorted by: [ date ] [ thread ] [ subject ] [ author ] [ attachment ]

Hi all

Thanks to those who have replied so far (original question below). They
have been either 'the files must be sparse' or 'the tape drive is doing
the compression'. I don't think the files are sparse as the big ones
are already compressed/gzipped.

I believe the TL891 (i.e., the TZ89) is a 35/70 GB tape drive (not a
40/80 as I indicated - even more perplexing that I seem to be able to
fit 108 GB on it). I had assumed that a 35/70 GB tape drive will give
me a capacity of 35 GB per tape uncompressed, or "up to" 70 GB
compressed, given the right media.

Or is it that it will give me 35 GB uncompressed on a DLT 3 or 70 GB
uncompressed on a DLT 4?

If the latter, then maybe I can get 108 GB compressed on a single DLT4
tape, but their compression algorithm must be pretty nifty!

In answer to other questions, the OS is DU 4.0E and the tape is a fresh
one out of the box. I did a -v on the vdump and recorded the screen
output to a file, see all the filenames go by and no error messages.

Thanks
John

-----Original Message-----
From: Speakman, John
Sent: Thursday, November 21, 2002 9:22 AM
To: tru64-unix-managers
Cc: Speakman, John
Subject: is vdump compressing data even when I don't ask it to?

     Hi all
     
     I find I can vdump a 108 GB fileset onto a TL891 library with a
     40/80GB TZ89 drive and it will stick the whole lot on one tape
without
     asking for a new tape.
     
     This is okay, even gratifying, as long as it's all really there.
But
     I don't specify compression (-C) , or a blocking factor (-b) , on
the
     vdump, and most of the data in this fileset is compressed or
gzipped
     already. Is vdump just doing some compression for me anyway?
     
     The 'man vdump' says:
     
     "Under normal usage, the vdump command uses a small amount of
     additional space on the storage device, typically less than 1
percent,
     when a fileset is backed up."
     
     But clearly this is not my experience...
     
     I am doing a 'vdump -D' on 4.0E. Will summarize.
     
     Thanks
     
     John Speakman
     Memorial Sloan-Kettering Cancer Center

• Next message: Kevin Beauchamp: "Problems adding DLT to AlphaServer 1000A"
• Previous message: Brehl, Blake: "SUMMARY: print leading or trailing lines in grep"
• Messages sorted by: [ date ] [ thread ] [ subject ] [ author ] [ attachment ]

This archive was generated by hypermail 2.1.7 : Sat Apr 12 2008 - 10:49:00 EDT