Why can't I trust rsync to be minimally as fast as cp? (I'm ignoring negligible differences for overhead.)
It seems to me like rsync is fairly slow on files with no content difference, but a changed timestamp.
If I make a file: cp -a testfile-100M destfile
And then I rsync them, I get what you would expect:
$ rsync -av testfile-100M destfile
sending incremental file list
sent 56 bytes received 12 bytes 8.00 bytes/sec
total size is 104857600 speedup is 1542023.53
But that's just because rsync is checking the size and the timestamp and skipping the file. What if I just change the timestamp?
$ touch testfile-100M
$ rsync -av testfile-100M destfile sending incremental file list
testfile-100M
sent 104870495 bytes received 31 bytes 113804.15 bytes/sec
total size is 104857600 speedup is 1.00
Also note that even though the speedup is 1, the inital copy took about 1/4 the time to complete than the final rsync, even though the contents are exactly the same. So what's going on here? Is it just all the overhead of doing the comparisons?
If that's the case, then when does rsync ever provide a performance advantage? Only when files are exactly the same on both sides?
For local files, if the size or mtime have changed, rsync by default just copies the whole thing without using its delta algorithm. You can turn this off with the --no-whole-file option, but for local copies this will typically be slower.
For the specific case of touching a file without changing it:
If you give the --size-only option, it will assume that files that have the same size are unchanged.
If you give the --checksum option, it will first hash the file to see if anything has changed, before copying it.
When the source and destination are both locally mounted filesystems rsync just copies the file(s) if the timestamps or sizes don't match. Rsync wins where you have large files with small differences and they are on machines separated by a low bandwidth link.
EDIT: Since someone felt the need to downvote this ancient answer... As to why rsync on local files might be slower than cp, there does not seem to be any good reason.
It appears the answer is that rsync does some extra steps in order to keep files in a consistent state, and not in a "partial-transferred" state while operating. Using the --inplace option removes this overhead.
Interestingly, for me rsync is about 4× faster than cp for copying to an external USB drive.
Related
I have about 700 folders containing relatively heavy files (10-40gb each), and I'm trying to make a compressed archive out of them.
When I use tar cf - ~/folder/* | pigz -p 30 > ~/folder/archive.tar.gz, I run out of my storage space (~13tb), which is larger than the size of my original files.
If I just tar the original files without compressing them, the resulting archive is about the same size as the sum of the original files (~8tb).
I tried compressing a small subset of my folders, and while pigz did not reduce the size by much, at least it did not increase the size...
What can be the issue here?
ps Not sure if it's relevant, but some of the heavy files in my folders are in a compressed format
I'm using rsync to backup some data from a remote host.
this is how I'm using the rsync cmd:
rsync --dry-run -avhi -e ssh --include-from=/home/rsync_list/test.txt root#10.10.4.61:/ /mnt/BACKUP/my_BACKUP/
this is the file /home/rsync_list/test.txt
+ /usr/acs/conf/**
+ /usr/acs/bin/**
+ /raid0/opmdps/TEMP_folder/**
- *
I want to copy only the listed folders excluding the remaining files.
I always get
receiving file list ... done
sent 103 bytes received 48 bytes 302.00 bytes/sec
total size is 0 speedup is 0.00 (DRY RUN)
Could you tell me what I'm doing wrong? How should I write the rsync command if I would like to sync, for example, only /raid0/opmdps/TEMP_folder/ without its subfolders?
I wonder if you really only tried with the command you posted?
Not only you are using "--dry-run" option, even the output indicates this:
total size is 0 speedup is 0.00 (DRY RUN)
Please consult the manpage:
-n, --dry-run perform a trial run with no changes made
https://linux.die.net/man/1/rsync
May I suggest you give it a run without --dry-run?
I need to compare two directories to validate a backup.
Say my directory looks like the following:
Filename Filesize Filename Filesize
user#main_server:~/mydir/ user#backup_server:~/mydir/
file1000.txt 4182410737 file1000.txt 4182410737
file1001.txt 8241410737 - <-- missing on backup_server!
... ...
file9999.txt 2410418737 file9999.txt 1111111111 <-- size != main_server
Is there a quick one liner that would get me close to output like:
Invalid Backup Files:
file1001.txt
file9999.txt
(with the goal to instruct the backup script to refetch these files)
I've tried to get variations of the following to no avail.
[main_server] $ rsync -n ~/mydir/ user#backup_server:~/mydir
I cannot do rsync to backup the directories itself because it takes way too long (8-24hrs). Instead I run multiple threads of scp to fetch files in batches. This completes regularly <1hr. However, occasionally I find a few files that were somehow missed (perhaps dropped connection).
Speed is a priority, so file sizes should be sufficient. But I'm open to including a checksum, provided it doesn't slow the process down like I find with rsync.
Here's my test process:
# Generate Large Files (1GB)
for i in {1..100}; do head -c 1073741824 </dev/urandom >foo-$i ; done
# SCP them from src to dest
for i in {1..100}; do ( scp ~/mydir/foo-$i user#backup_server:~/mydir/ & ) ; sleep 0.1 ; done
# Confirm destination has everything from source
# This is the point of the question. I've tried:
rsync -Sa ~/mydir/ user#backup_server:~/mydir
# Way too slow
What do you recommend?
By default, rsync uses the quick check method which only transfers files that differ in size or last-modified time. As you report that the sizes are unchanged, that would seem to indicate that the timestamps differ. Two options to handlel this are:
Use -p to preserve timestamps when transferring files.
Use --size-only to ignore timestamps and transfer only files that differ in size.
I'm using cwRsync 5.4.1 x86 Free under windows and trying to sync folder to network drive.
I execute following command:
rsync.exe -rLtv --delete --ignore-errors "/cygdrive/d/1/" "/cygdrive/z/ZipNB/"
Where D is local drive and Z is network drive (external HDD connected to router, RT-N16)
Executing it several times gives same result:
>rsync.exe -rLtv --delete --ignore-errors "/cygdrive/d/1/" "/cygdrive/z/ZipNB/"
sending incremental file list
./
1.pdf
sent 11,893,922 bytes received 38 bytes 1,829,840.00 bytes/sec
total size is 11,890,918 speedup is 1.00
I have one file in the folder and it sends its content each execution. File is same each time and was not changed in the middle.
If I add additional parameter --size-only it works as expected:
>rsync.exe -rLtv --delete --ignore-errors --size-only "/cygdrive/d/1/" "/cygdrive/z/ZipNB/"
sending incremental file list
./
sent 72 bytes received 22 bytes 188.00 bytes/sec
total size is 11,890,918 speedup is 126,499.13
DIR for both directories:
D:\1>dir
Volume in drive D is XXX
Volume Serial Number is XXXX-XXX
Directory of D:\1
08.12.2016 10:04 <DIR> .
08.12.2016 10:04 <DIR> ..
24.11.2016 18:31 11 890 918 1.pdf
1 File(s) 11 890 918 bytes
Z:\ZipNB>dir
Volume in drive Z is BackUp (at Portable)
Volume Serial Number is XXXX-XXX
Directory of Z:\ZipNB
08.12.2016 10:04 <DIR> .
08.10.2016 20:40 <DIR> ..
24.11.2016 18:31 11 890 918 1.pdf
1 File(s) 11 890 918 bytes
I'm not sure but as I'm aware of rsync by default makes verification of file by modification time and size. Both files seems identical. But it seems like cwRsync for some reason gets/sets wrong modification date on file at Z drive. cwRsync works correctly if both directories are on local drive. It happens only with network drive.
In windows properties there is difference in modification time in 1 second, which can cause the problem.
I took only 1 file as an example only to simplify output, the situation is same heaving any amount of different files. It always sends full content of each file.
What can be wrong here, and how I can fix it?
I'm guessing the HDD on the network share uses FAT, because from File Times:
For example, the resolution of create time on FAT is 10 milliseconds,
while write time has a resolution of 2 seconds and access time has a
resolution of 1 day, so it is really the access date.
That would explain the time difference.
And for this kind of reason rsync added the --modify-window option:
-#, --modify-window
When comparing two timestamps, rsync treats the timestamps as being equal if they differ by no more than the modify-window value.
The default is 0, which matches just integer seconds. If you specify a
negative value (and the receiver is at least version 3.1.3) then
nanoseconds will also be taken into account. Specifying 1 is useful
for copies to/from MS Windows FAT filesystems, because FAT represents
times with a 2-second resolution (allowing times to differ from the
original by up to 1 second).
So try to add -#1 to your command.
Here is my problem, I have a set of big gz log files, the very first info in the line is a datetime text, e.g.: 2014-03-20 05:32:00.
I need to check what set of log files holds a specific data.
For the init I simply do a:
'-query-data-'
zgrep -m 1 '^20140320-04' 20140320-0{3,4}*gz
BUT HOW to do the same with the last line without process the whole file as would be done with zcat (too heavy):
zcat foo.gz | tail -1
Additional info, those logs are created with the data time of it's initial record, so if I want to query logs at 14:00:00 I have to search, also, in files created BEFORE 14:00:00, as a file would be created at 13:50:00 and closed at 14:10:00.
The easiest solution would be to alter your log rotation to create smaller files.
The second easiest solution would be to use a compression tool that supports random access.
Projects like dictzip, BGZF, and csio each add sync flush points at various intervals within gzip-compressed data that allow you to seek to in a program aware of that extra information. While it exists in the standard, the vanilla gzip does not add such markers either by default or by option.
Files compressed by these random-access-friendly utilities are slightly larger (by perhaps 2-20%) due to the markers themselves, but fully support decompression with gzip or another utility that is unaware of these markers.
You can learn more at this question about random access in various compression formats.
There's also a "Blasted Bioinformatics" blog by Peter Cock with several posts on this topic, including:
BGZF - Blocked, Bigger & Better GZIP! – gzip with random access (like dictzip)
Random access to BZIP2? – An investigation (result: can't be done, though I do it below)
Random access to blocked XZ format (BXZF) – xz with improved random access support
Experiments with xz
xz (an LZMA compression format) actually has random access support on a per-block level, but you will only get a single block with the defaults.
File creation
xz can concatenate multiple archives together, in which case each archive would have its own block. The GNU split can do this easily:
split -b 50M --filter 'xz -c' big.log > big.log.sp.xz
This tells split to break big.log into 50MB chunks (before compression) and run each one through xz -c, which outputs the compressed chunk to standard output. We then collect that standard output into a single file named big.log.sp.xz.
To do this without GNU, you'd need a loop:
split -b 50M big.log big.log-part
for p in big.log-part*; do xz -c $p; done > big.log.sp.xz
rm big.log-part*
Parsing
You can get the list of block offsets with xz --verbose --list FILE.xz. If you want the last block, you need its compressed size (column 5) plus 36 bytes for overhead (found by comparing the size to hd big.log.sp0.xz |grep 7zXZ). Fetch that block using tail -c and pipe that through xz. Since the above question wants the last line of the file, I then pipe that through tail -n1:
SIZE=$(xz --verbose --list big.log.sp.xz |awk 'END { print $5 + 36 }')
tail -c $SIZE big.log.sp.xz |unxz -c |tail -n1
Side note
Version 5.1.1 introduced support for the --block-size flag:
xz --block-size=50M big.log
However, I have not been able to extract a specific block since it doesn't include full headers between blocks. I suspect this is nontrivial to do from the command line.
Experiments with gzip
gzip also supports concatenation. I (briefly) tried mimicking this process for gzip without any luck. gzip --verbose --list doesn't give enough information and it appears the headers are too variable to find.
This would require adding sync flush points, and since their size varies on the size of the last buffer in the previous compression, that's too hard to do on the command line (use dictzip or another of the previously discussed tools).
I did apt-get install dictzip and played with dictzip, but just a little. It doesn't work without arguments, creating a (massive!) .dz archive that neither dictunzip nor gunzip could understand.
Experiments with bzip2
bzip2 has headers we can find. This is still a bit messy, but it works.
Creation
This is just like the xz procedure above:
split -b 50M --filter 'bzip2 -c' big.log > big.log.sp.bz2
I should note that this is considerably slower than xz (48 min for bzip2 vs 17 min for xz vs 1 min for xz -0) as well as considerably larger (97M for bzip2 vs 25M for xz -0 vs 15M for xz), at least for my test log file.
Parsing
This is a little harder because we don't have the nice index. We have to guess at where to go, and we have to err on the side of scanning too much, but with a massive file, we'd still save I/O.
My guess for this test was 50000000 (out of the original 52428800, a pessimistic guess that isn't pessimistic enough for e.g. an H.264 movie.)
GUESS=50000000
LAST=$(tail -c$GUESS big.log.sp.bz2 \
|grep -abo 'BZh91AY&SY' |awk -F: 'END { print '$GUESS'-$1 }')
tail -c $LAST big.log.sp.bz2 |bunzip2 -c |tail -n1
This takes just the last 50 million bytes, finds the binary offset of the last BZIP2 header, subtracts that from the guess size, and pulls that many bytes off of the end of the file. Just that part is decompressed and thrown into tail.
Because this has to query the compressed file twice and has an extra scan (the grep call seeking the header, which examines the whole guessed space), this is a suboptimal solution. See also the below section on how slow bzip2 really is.
Perspective
Given how fast xz is, it's easily the best bet; using its fastest option (xz -0) is quite fast to compress or decompress and creates a smaller file than gzip or bzip2 on the log file I was testing with. Other tests (as well as various sources online) suggest that xz -0 is preferable to bzip2 in all scenarios.
————— No Random Access —————— ——————— Random Access ———————
FORMAT SIZE RATIO WRITE READ SIZE RATIO WRITE SEEK
————————— ————————————————————————————— —————————————————————————————
(original) 7211M 1.0000 - 0:06 7211M 1.0000 - 0:00
bzip2 96M 0.0133 48:31 3:15 97M 0.0134 47:39 0:00
gzip 79M 0.0109 0:59 0:22
dictzip 605M 0.0839 1:36 (fail)
xz -0 25M 0.0034 1:14 0:12 25M 0.0035 1:08 0:00
xz 14M 0.0019 16:32 0:11 14M 0.0020 16:44 0:00
Timing tests were not comprehensive, I did not average anything and disk caching was in use. Still, they look correct; there is a very small amount of overhead from split plus launching 145 compression instances rather than just one (this may even be a net gain if it allows an otherwise non-multithreaded utility to consume multiple threads).
Well, you can access randomly a gzipped file if you previously create an index for each file ...
I've developed a command line tool which creates indexes for gzip files which allow for very quick random access inside them:
https://github.com/circulosmeos/gztool
The tool has two options that may be of interest for you:
-S option supervise a still-growing file and creates an index for it as it is growing - this can be useful for gzipped rsyslog files as reduces to zero in the practice the time of index creation.
-t tails a gzip file: this way you can do: $ gztool -t foo.gz | tail -1
Please, note that if the index doesn't exists, this will consume the same time as a complete decompression: but as the index is reusable, next searches will be greatly reduced in time!
This tool is based on zran.c demonstration code from original zlib, so there's no out-of-the-rules magic!