From: Goffredo Baroncelli <kreijack@inwind.it>
To: Roman Mamedov <rm@romanrm.ru>
Cc: kreijack@libero.it, "Sébastien Maury" <sebastien.maury@inserm.fr>,
linux-btrfs@vger.kernel.org, "Hugo Mills" <hugo@carfax.org.uk>
Subject: Re: [RFC] btrfs fi df output [Was Re: BTRF - Storage Usage]
Date: Fri, 28 Sep 2012 18:44:07 +0200 [thread overview]
Message-ID: <5065D3D7.8080101@inwind.it> (raw)
In-Reply-To: <20120928091759.6d096016@natsu>
On 09/28/2012 05:17 AM, Roman Mamedov wrote:
> On Thu, 27 Sep 2012 23:02:35 +0200
> Goffredo Baroncelli<kreijack@libero.it> wrote:
>
>> Sorry for the space error:
>> Below a more correct example
>>
>> $ btrfs filesystem disk-free /
>> Summary:
>> Total: 135.00GB
>> Allocated: 10.51GB
>> Unallocated: 124.49GB
>> Free_(Estimated) 86.56GB
>> Average_disk_efficiency: 62 %
>
> How do you estimate "Free" here? Sorry I didn't check the source code in git,
> but from the "Details" below nothing leads me to believe that this FS is
> doomed to only be able to usefully utilize only ~86GB of the partition, and not
> more.
The estimation is made on the basis of the real allocated space on the
disk and the available space.
In the example we know that BTRFS allocate:
- 4GB in Single mode (4GB available, 2.16GB used)
- 16MB in DUP mode (so 16/2=8MB available, 4kb used)
- 4MB in Single mode (4MB available)
- 6GB in DUP mode (6/2=3GB available, 429MB used)
- 8MB in Single mode (8MB available)
So BTRFS allocated on disk 4GB+16MB+4MB+6GB+8MB = ~10GB, but the space
availabled (regarding these allocated chunks) is 4GB+8MB+4MB+3GB+8MB = ~7GB.
This means that the ration of space physically allocated on the disk and
the space available is 7GB/10GB = 0.7 . So on 135GB of disk, only 94GB
are available.
Yes my previous 0.62 was wrong. The real ratio is 0.7.
> Are you ready to answer the flood of questions from people why their disk is
> only 62% efficient, and how to tune it to 100%? :-)
I don't understand your question: by default BTRFS store all metadata
DUP-ed, this means that on the disk the space allocated are 2 times the
space required. Because on BTRFS the metadata are a lot, this means that
BTRFS is not so efficiency as other file-systems. This is a well know fact.
If you want to use all the space with the maximum efficiency, you could
format the filesystem with the options "-m single".
>
> Why use underscores instead of spaces?
Simplify the parsing in scripts
>
>>
>> Details:
>> Chunk-type Mode Allocated Used Free
>> ---------- ---- --------- -------- ---------
>> Data Single 4.01GB 2.16GB 1.87GB
>> System DUP 16.00MB 4.00KB 7.99MB
>> System Single 4.00MB 0.00 4.00MB
>> Metadata DUP 6.00GB 429.16MB 2.57GB
>> Metadata Single 8.00MB 0.00 8.00MB
>
next prev parent reply other threads:[~2012-09-28 16:44 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-27 10:44 BTRF - Storage Usage Sébastien Maury
2012-09-27 11:09 ` Hugo Mills
2012-09-27 11:25 ` Sébastien Maury
2012-09-27 11:43 ` Hugo Mills
2012-09-27 11:52 ` Sébastien Maury
2012-09-27 20:39 ` [RFC] btrfs fi df output [Was Re: BTRF - Storage Usage] Goffredo Baroncelli
2012-09-27 21:02 ` Goffredo Baroncelli
2012-09-28 3:17 ` Roman Mamedov
2012-09-28 8:58 ` Hugo Mills
2012-09-28 17:27 ` Goffredo Baroncelli
2012-09-28 20:13 ` Hugo Mills
2012-09-28 21:26 ` Goffredo Baroncelli
2012-09-29 7:19 ` Goffredo Baroncelli
2012-09-29 9:59 ` Sébastien Maury
2012-09-29 11:51 ` Goffredo Baroncelli
2012-11-12 18:16 ` Jan Engelhardt
2012-09-28 16:44 ` Goffredo Baroncelli [this message]
2012-09-28 18:02 ` Roman Mamedov
2012-09-28 19:38 ` Goffredo Baroncelli
2012-09-28 20:20 ` Hugo Mills
2012-09-28 21:26 ` Wade Cline
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