I find myself having to compress a number of very large files (80-ish GB), and I am surprised at the (lack of) speed my system is exhibiting. I get about 500 MB / min conversion speed; using top
, I seem to be using a single CPU at approximately 100%.
I am pretty sure it's not (just) disk access speed, since creating a tar
file (that's how the 80G file was created) took just a few minutes (maybe 5 or 10), but after more than 2 hours my simple gzip command is still not done.
In summary:
tar -cvf myStuff.tar myDir/*
Took <5 minutes to create an 87 G tar file
gzip myStuff.tar
Took two hours and 10 minutes, creating a 55G zip file.
My question: Is this normal? Are there certain options in gzip
to speed things up? Would it be faster to concatenate the commands and use tar -cvfz
? I saw reference to pigz
- Parallel Implementation of GZip - but unfortunatly I cannot install software on the machine I am using, so that is not an option for me. See for example this earlier question.
I am intending to try some of these options myself and time them - but it is quite likely that I will not hit "the magic combination" of options. I am hoping that someone on this site knows the right trick to speed things up.
When I have the results of other trials available I will update this question - but if anyone has a particularly good trick available, I would really appreciate it. Maybe the gzip just takes more processing time than I realized...
UPDATE
As promised, I tried the tricks suggsted below: change the amount of compression, and change the destination of the file. I got the following results for a tar that was about 4.1GB:
flag user system size sameDisk
-1 189.77s 13.64s 2.786G +7.2s
-2 197.20s 12.88s 2.776G +3.4s
-3 207.03s 10.49s 2.739G +1.2s
-4 223.28s 13.73s 2.735G +0.9s
-5 237.79s 9.28s 2.704G -0.4s
-6 271.69s 14.56s 2.700G +1.4s
-7 307.70s 10.97s 2.699G +0.9s
-8 528.66s 10.51s 2.698G -6.3s
-9 722.61s 12.24s 2.698G -4.0s
So yes, changing the flag from the default -6
to the fastest -1
gives me a 30% speedup, with (for my data) hardly any change to the size of the zip file. Whether I'm using the same disk or another one makes essentially no difference (I would have to run this multiple times to get any statistical significance).
If anyone is interested, I generated these timing benchmarks using the following two scripts:
#!/bin/bash
# compare compression speeds with different options
sameDisk='./'
otherDisk='/tmp/'
sourceDir='/dirToCompress'
logFile='./timerOutput'
rm $logFile
for i in {1..9}
do /usr/bin/time -a --output=timerOutput ./compressWith $sourceDir $i $sameDisk $logFile
do /usr/bin/time -a --output=timerOutput ./compressWith $sourceDir $i $otherDisk $logFile
done
And the second script (compressWith
):
#!/bin/bash
# use: compressWith sourceDir compressionFlag destinationDisk logFile
echo "compressing $1 to $3 with setting $2" >> $4
tar -c $1 | gzip -$2 > $3test-$2.tar.gz
Three things to note:
- Using
/usr/bin/time
rather thantime
, since the built-in command ofbash
has many fewer options than the GNU command - I did not bother using the
--format
option although that would make the log file easier to read - I used a script-in-a-script since
time
seemed to operate only on the first command in a piped sequence (so I made it look like a single command...).
With all this learnt, my conclusions are
- Speed things up with the
-1
flag (accepted answer) - Much more time is spend compressing the data than reading from disk
- Invest in faster compression software (
pigz
seems like a good choice). - If you have multiple files to compress you can put each
gzip
command in its own thread and use more of the available CPU (poor man’spigz
)
Thanks everyone who helped me learn all this!
$> gzip -c myStuff.tar | pv -r -b > myStuff.tar.gz
will show you how fast your machine is compressing the stuff. side-note2: store the result onto a different disc.man
page, and I didn't read that far (because it's sorted by 'single letter command', which is-#
). That will teach me to RTFM! This will be the next thing I try!pigz
and run it from wherever you happened to build it, without installing it. If there is no compiler, you could cross-compile it on another computer, although that's starting to get into more effort than might be worth it. (Depending on just how badly you need this compression to run faster, I guess.)