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...


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:

# compare compression speeds with different options
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

And the second script (compressWith):

# 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:

  1. Using /usr/bin/time rather than time, since the built-in command of bash has many fewer options than the GNU command
  2. I did not bother using the --format option although that would make the log file easier to read
  3. 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

  1. Speed things up with the -1 flag (accepted answer)
  2. Much more time is spend compressing the data than reading from disk
  3. Invest in faster compression software (pigz seems like a good choice).
  4. 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’s pigz)

Thanks everyone who helped me learn all this!

  • tar -cvf doesn't do any compression so it will be quicker
    – parkydr
    May 3, 2013 at 17:23
  • 2
    @Floris: what kind of data are you trying to compress? side-note: $> 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.
    – akira
    May 3, 2013 at 17:31
  • 3
    Sorry, I misread your question. gzip has the --fast option to select the fastest compression
    – parkydr
    May 3, 2013 at 17:32
  • 1
    @parkydr : The --fast option is one I didn't know about... it's the very last one in the 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!
    – Floris
    May 3, 2013 at 17:45
  • 2
    Note that if a suitable compiler is available on the machine, and the filesystem permissions are not set to prohibit executing binaries from the directories you have access to, you can compile 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.)
    – David Z
    May 3, 2013 at 19:42

4 Answers 4


You can change the speed of gzip using --fast --best or -# where # is a number between 1 and 9 (1 is fastest but less compression, 9 is slowest but more compression). By default gzip runs at level 6.

  • I use 7zip on a Win10 virtual machine. Going from default 5 to the fastest 1 compression the speed went from some 7MB/s to about 48MB/s. The compression ratio went from about 18% to 30%, which is acceptable in my case. The 4 virtual CPUs are pegged at 100%. Jul 1, 2022 at 13:27

The reason tar takes so little time compared to gzip is that there's very little computational overhead in copying your files into a single file (which is what it does). gzip on the otherhand, is actually using compression algorithms to shrink the tar file.

The problem is that gzip is constrained (as you discovered) to a single thread.

Enter pigz, which can use multiple threads to perform the compression. An example of how to use this would be:

tar -c --use-compress-program=pigz -f tar.file dir_to_zip

There is a nice succint summary of the --use-compress-program option over on a sister site.

  • Thanks for your answer and links. I actually mentioned pigz in the question.
    – Floris
    Feb 29, 2016 at 12:55
  • 1
    This is the correct answer here..!
    – stolsvik
    Nov 30, 2016 at 8:19

I seem to be using a single CPU at approximately 100%.

That implies there isn't an I/O performance issue but that the compression is only using one thread (which will be the case with gzip).

If you manage to achieve the access/agreement needed to get other tools installed, then 7zip also supports multiple threads to take advantage of multi core CPUs, though I'm not sure if that extends to the gzip format as well as its own.

If you are stuck to using just gzip for the time being and have multiple files to compress, you could try compressing them individually - that way you'll use more of that multi-core CPU by running more than one process in parallel. Be careful not to overdo it though because as soon as you get anywhere near the capacity of your I/O subsystem performance will drop off precipitously (to lower than if you were using one process/thread) as the latency of head movements becomes a significant bottleneck.

  • 1
    thanks for your input. You gave me an idea (for which you get an upvote): since I have multiple archives to create I can just write the individual commands followed by a & - then let the system take care of it from there. Each will run on its own processor, and since I spend far more time on compression than on I/O, it will take the same time to do one as to do all 10 of them. So I get "multi core performance" from an executable that's single threaded...
    – Floris
    May 9, 2013 at 15:09

One can exploit the number of process available as well in pigz which is usually faster performance as shown in the following command

tar cf - directory to archive | pigz -0 -p largenumber > mydir.tar.gz

Example - tar cf - patha | pigz -0 -p 32 > patha.tar.gz

This is probably faster than the methods suggested in the post as -p is the number of processes one can run. In my personal experience setting a very large value doesnt hurt performance if the directory to be archived consists of a large number of small files. Else the default value considered is 8. For large files, my recommendation would be to set this value as the total number of threads supported on the system.

Example setting a value of p = 32 in case of a 32 CPU machine helps.

0 is meant for the fastest pigz compression as it doesnt compress the archive and rather is focussed on speed. Default value is 6 for compression.

  • 1
    Why would you use pigz at all if you weren't planning to compress the archive? Dec 9, 2020 at 11:42

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