On Aug 26, 2007, at 8:09 PM, Jean-David Beyer wrote:
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Bruce Momjian wrote:
Jean-David Beyer wrote:
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When I make a backup of a database, I put the output file
directly on
magnetic tape; i.e., my command looks like this:
pg_dump --file=/dev/st0 ....
This way I do not have to worry if the total backup exceeds the
size of a
file system, and it saves me the trouble of copying it to the
tape as a
separate step. My current tapes will hold 20 GBytes raw or
40GBytes if I
enable hardware compression (assuming 2:1 compression happens).
Now it says
in the documentation that if I use format c it will compress the
data in
software, so I doubt the hardware compression will do much.
I do not know what blocksize pg_dump uses, or if it insists on a
particular
blocksize on input.
Now my tape drive will work with any blocksize, but prefers 65536-
byte
blocks. I do not see any options for this in pg_dump, but I could
pipe the
output of pg_dump through dd I suppose to make any blocksize I want.
On the way back, likewise I could pipe the tape through dd before
giving it
to pg_restore.
Does pg_dump care what blocksize it gets? If so, what is it?
I assume you could pipe pg_dump into dd and specify the block size in
dd.
Of course on the way out I can do that.
The main question is, If I present pg_restore with a 65536-byte
blocksize
and it is expecting, e.g., 1024-bytes, will the rest of each block get
skipped? I.e., do I have to use dd on the way back too? And if so,
what
should the blocksize be?
Postgres (by default) uses 8K blocks.
Erik Jones
Software Developer | Emma®
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