[rescue] Block size and the single DD - some test results
Sheldon T. Hall
shel at cmhcsys.com
Wed Feb 11 23:18:46 CST 2004
This is _very_ interesting.
Taking suggestions from several list members, I'm doing some speed tests to
determine how better to use my new DLT2000xt tape drives.
rtfm SPARCclassic, 128 MB RAM, internal 4.5 GB HD,
external DLT200xt on SBUS FW SE SCSI bus.
blinky SGI Indigo^2, R4k/200, 384 MB RAM, 2 internal
4.5 GB HD
tandem SGI Chalenge L, 4xR4k/150, 1.5 GB RAM, several
internal 18 GB SE-FW HD and internal DLT200xt
on SE FW bus.
Currently, the drive I use is hooked to rtfm, and it doesn't stream.
Raw disk speeds
Executing dd to read 2048 64k blocks (134,217,728 bytes) from a raw disk
partition and write them to /dev/null took ...
rtfm 40 seconds
blinky 20 seconds
tandem 11 seconds
Raw tape speed
Using the same dd command but directing the output directly to the
appropriate local tape device:
rtfm 1:35 - mostly streamed
blinky no attached tape
tandem 1:48 - can't tell about streaming, but it must not have
Executing xfsdump to read 45,359,864 bytes in a filesystem on a remote
machine and write them to /dev/null on the local machine took ...
Taking the output of that same xfsdump, piping it over the network through
dd on the local machine and writing it to /dev/null took ...
blinky to rtfm 1:18
tandem to rtfm 1:17
tandem to blinky 1:16
tinkers to evers to chance Double Play!
As several have suggested, it looks like the SPARCclassic isn't fast enough
to stream the DLT tape from its local filesystems, even with DD.
All this was with a 10baseT network, and that looks like a limiting factor.
I'll have to do some more experimenting to see if changing the networking to
100baseT will make enough difference with the remote backups, or if moving
the backups to the Challenge will improve things.
Thanks for the ideas. More when I know it.
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