You can fill up an ext3 filesystem with the following command:
dd if=/dev/zero of=delme.dat
You can't really fill up a ZFS filesystme that way. I guess you could,
but I've never had the patience -- when several GB worth of zeroes takes
1kb worth of data, then it would take a very long time.
AFAIK, ext3 supports sparse files just like it should -- but it doesn't
dynamically figure out what to write based on the contents of the file.
-Luke
Jeremy F. wrote:
> This may be my ignorance, but I thought all modern unix filesystems created
> sparse files in this way?
>
>
> -----Original Message-----
> From: Stuart Anderson <[EMAIL PROTECTED]>
>
> Date: Mon, 14 Apr 2008 15:45:03
> To:Luke Scharf <[EMAIL PROTECTED]>
> Cc:zfs-discuss@opensolaris.org
> Subject: Re: [zfs-discuss] Confused by compressratio
>
>
> On Mon, Apr 14, 2008 at 05:22:03PM -0400, Luke Scharf wrote:
>
>> Stuart Anderson wrote:
>>
>>> On Mon, Apr 14, 2008 at 09:59:48AM -0400, Luke Scharf wrote:
>>>
>>>
>>>> Stuart Anderson wrote:
>>>>
>>>>
>>>>> As an artificial test, I created a filesystem with compression enabled
>>>>> and ran "mkfile 1g" and the reported compressratio for that filesystem
>>>>> is 1.00x even though this 1GB file only uses only 1kB.
>>>>>
>>>>>
>>>>>
>>>> ZFS seems to treat files filled with zeroes as sparse files, regardless
>>>> of whether or not compression is enabled. Try "dd if=/dev/urandom
>>>> of=1g.dat bs=1024 count=1048576" to create a file that won't exhibit
>>>> this behavior. Creating this file is a lot slower than writing zeroes
>>>> (mostly due to the speed of the urandom device), but ZFS won't treat it
>>>> like a sparse file, and it won't compress very well either.
>>>>
>>>>
>>> However, I am still trying to reconcile the compression ratio as
>>> reported by compressratio vs the ratio of file sizes to disk blocks
>>> used (whether or not ZFS is creating sparse files).
>>>
>>>
>> Can you describe the data you're storing a bit? Any big disk images?
>>
>>
>
> Understanding the "mkfile" case would be a start, but the initial filesystem
> that started my confusion is one that has a number of ~50GByte mysql database
> files as well as a number of application code files.
>
> Here is another simple test to avoid any confusion/bugs related to NULL
> character sequeneces being compressed to nothing versus being treated
> as sparse files. In particular, a 2GByte file full of the output of
> /bin/yes:
>
>
>> zfs create export-cit/compress
>> cd /export/compress
>> /bin/df -k .
>>
> Filesystem kbytes used avail capacity Mounted on
> export-cit/compress 1704858624 55 1261199742 1% /export/compress
>
>> zfs get compression export-cit/compress
>>
> NAME PROPERTY VALUE SOURCE
> export-cit/compress compression on inherited from
> export-cit
>
>> /bin/yes | head -1073741824 > yes.dat
>> /bin/ls -ls yes.dat
>>
> 185017 -rw-r--r-- 1 root root 2147483648 Apr 14 15:31 yes.dat
>
>> /bin/df -k .
>>
> Filesystem kbytes used avail capacity Mounted on
> export-cit/compress 1704858624 92563 1261107232 1% /export/compress
>
>> zfs get compressratio export-cit/compress
>>
> NAME PROPERTY VALUE SOURCE
> export-cit/compress compressratio 28.39x -
>
> So compressratio reports 28.39, but the ratio of file size to used disk for
> the only regular file on this filesystem, i.e., excluding the initial 55kB
> allocated for the "empty" filesystem is:
>
> 2147483648 / (185017 * 512) = 22.67
>
>
> Calculated another way from "zfs list" for the entire filesystem:
>
>
>> zfs list /export/compress
>>
> NAME USED AVAIL REFER MOUNTPOINT
> export-cit/compress 90.4M 1.17T 90.4M /export/compress
>
> is 2GB/90.4M = 2048 / 90.4 = 22.65
>
>
> That still leaves me puzzled what the precise definition of compressratio is?
>
>
> Thanks.
>
> ---
> Stuart Anderson [EMAIL PROTECTED]
> http://www.ligo.caltech.edu/~anderson
> _______________________________________________
> zfs-discuss mailing list
> zfs-discuss@opensolaris.org
> http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
>
_______________________________________________
zfs-discuss mailing list
zfs-discuss@opensolaris.org
http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
