Process order of scripts

Fixit7 · 03-10-2016, 03:37 PM

Does this script process the copying BEFORE it sends the second date to the file ?

Because my results are not true.

Quote:

date "+ %m/%d/%y %r" >> Speed.txt
gxmessage -timeout 2 "Copying 819 Mb file to sdb2."
cp largefile /mnt/sdb2
date "+ %m/%d/%y %r" >> Speed.txt

03/10/16 03:31:30 PM
03/10/16 03:31:56 PM

26 seconds to copy a 819 Mb file to an external drive ??

Keith Hedger · 03-10-2016, 04:48 PM

If the external drive was a usb it may have been asleep and needed to wake up before the copy could take place, also you would get better results when timing a command to use

Code:

time cp largefile /mnt/sdb2

as this gives the time the command took to run.

rknichols · 03-10-2016, 04:51 PM

As far as the cp program is concerned, the job is done. In reality, that data is sitting in the kernel's buffer cache and being flushed out to the disk in the background. If you've got a lot of memory, there can be gigabytes of data in those buffers. Run sync or unmount the filesystem to see how long the operation really takes.

Fixit7 · 03-10-2016, 05:07 PM

Thanks.

Quote:

TextFile='Speed.txt'

date "+ %m/%d/%y %r" >> $TextFile
gxmessage -timeout 2 "Copying largefile to sdb2."
time (cp largefile /mnt/sdb2) >> $TextFile 2>&1
echo ........................ >> $TextFile
#rm largefile
rm /mnt/sdb2/largefile

rknichols · 03-10-2016, 06:52 PM

Quote:

Originally Posted by Fixit7

Code:

TextFile='Speed.txt'

date "+ %m/%d/%y %r" >> $TextFile
gxmessage -timeout 2 "Copying largefile to sdb2."
time (cp largefile /mnt/sdb2) >> $TextFile 2>&1
echo ........................ >> $TextFile
#rm largefile
rm /mnt/sdb2/largefile

And the result of that is???

Note also that largefile might never be written to /mnt/sdb2. If you delete the file before the buffers have been flushed out, any pending writes are cancelled, and the data is never written to the drive. That happens a lot with short-lived files in /tmp, and is part of the reason that putting /tmp on a disk vs. putting /tmp in a tmpfs in RAM that is potentially swapped out to disk doesn't make a large difference in the amount of disk I/O that is performed.

Note: Please do not use [QUOTE] ... [/QUOTE] tags for purposes other than quoting other posts. It makes it hard to quote your content in a reply. Use [CODE] ... [/CODE] tags instead.

Fixit7 · 03-10-2016, 09:25 PM

So would a sync before the deletion flush all the buffers ?

Fixit7 · 03-10-2016, 09:26 PM

I see no difference ?

Quote:

Originally Posted by Fixit7

So would a sync before the deletion flush all the buffers ?

Code:

code

rknichols · 03-11-2016, 08:08 AM

Quote:

Originally Posted by Fixit7

So would a sync before the deletion flush all the buffers ?

It would, but you have to include the time it takes for the sync to return. The cp command will still finish before the buffers are flushed, just as it did before.

Code:

time (cp largefile /mnt/sdb2; sync)

Fixit7 · 03-11-2016, 10:46 AM

So, there is no way to get an accurate reading.

Fixit7 · 03-11-2016, 10:54 AM

There is only .06 secs difference.

It looks like the buffers are flushed

Quote:

Time with largefile being deleted

03/11/16 10:48:10 AM

real 0m2.573s
user 0m0.000s
sys 0m0.387s

Time without large file being deleted

........................
03/11/16 10:49:13 AM

real 0m1.307s
user 0m0.010s
sys 0m0.317s
........................

Code:

TextFile='Speed.txt'

date "+ %m/%d/%y %r" >> $TextFile
gxmessage -timeout 2 "Copying largefile to sdb2."
time (cp largefile /mnt/sdb2) >> $TextFile 2>&1
# Write all buffered blocks to disk
echo ........................ >> $TextFile
sync
sleep 5
#rm largefile
#rm /mnt/sdb2/largefile

pan64 · 03-11-2016, 11:13 AM

you need to check the real time (see man time about the meaning real/user/sys)

Fixit7 · 03-11-2016, 04:11 PM

Interesting, so the time is half when the file is not deleted.

I'll read up on real,user,sys.