On 12/27/2014 06:00 AM, Robert White wrote:
On 12/27/2014 05:16 AM, Martin Steigerwald wrote:
It can easily be reproduced without even using Virtualbox, just by a nice
simple fio job.
TL;DR: If you want a worst-case example of consuming a BTRFS filesystem
with one single file...
#!/bin/bash
# not tested, so correct any syntax errors
typeset -i counter
for ((counter=250;counter>0;counter--)); do
dd if=/dev/urandom of=/some/file bs=4k count=$counter
done
exit 0
Slight correction: you need to prevent the truncate dd performs by
default, and flush the data and metadata to disk between after each
invocatoin. So you need the "conv=" flags.
for ((counter=250;counter>0;counter--)); do
dd if=/dev/urandom of=some_file conv=notrunc,fsync bs=4k count=$counter
done
Each pass over /some/file is 4k shorter than the previous one, but none
of the extents can be deallocated. File will be 1MiB in size and usage
will be something like 125.5MiB (if I've done the math correctly).
larger values of counter will result in exponentially larger amounts of
waste.
Doing the bad things is very bad...
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