True size of btrfs data chunk

True size of btrfs data chunk

[Timofey Titovets]

Hi, as wiki say https://btrfs.wiki.kernel.org/index.php/Glossary:
A part of a block group. Chunks are either 1 GiB in size (for data) or
256 MiB (for metadata).

Btrfs tools show me that allocated size is not 1GiB aligned, things
are changes? I miss something?

# btrfs fi df /; btrfs fi usage /;
Data, single: total=1.41GiB, used=704.47MiB
System, single: total=32.00MiB, used=16.00KiB
Metadata, single: total=256.00MiB, used=54.30MiB
GlobalReserve, single: total=32.00MiB, used=0.00B
Overall:
   Device size:                   4.00GiB
   Device allocated:              1.69GiB
   Device unallocated:            2.31GiB
   Device missing:                  0.00B
   Used:                        758.79MiB
   Free (estimated):              3.03GiB      (min: 3.03GiB)
   Data ratio:                       1.00
   Metadata ratio:                   1.00
   Global reserve:               32.00MiB      (used: 0.00B)

Data,single: Size:1.41GiB, Used:704.47MiB
  /dev/sda1       1.41GiB

Metadata,single: Size:256.00MiB, Used:54.30MiB
  /dev/sda1     256.00MiB

System,single: Size:32.00MiB, Used:16.00KiB
  /dev/sda1      32.00MiB

Unallocated:
  /dev/sda1       2.31GiB

Thanks.
-- 
Have a nice day,
Timofey.

Re: True size of btrfs data chunk

[Austin S. Hemmelgarn]

On 2016-11-29 09:32, Timofey Titovets wrote:
> Hi, as wiki say https://btrfs.wiki.kernel.org/index.php/Glossary:
> A part of a block group. Chunks are either 1 GiB in size (for data) or
> 256 MiB (for metadata).
This is only about the normal case.  Chunks are variable in size.  In 
most cases, data chunks will be 1GB and metadata 256MB.  They will 
however be smaller if there isn't enough space left for a full chunk, 
and will get larger as well once you get past a certain filesystem size 
(I don't remember the exact size, but I've seen people talking about big 
(double digit TB sized) filesystems with 5GB+ sized data chunks).
>
> Btrfs tools show me that allocated size is not 1GiB aligned, things
> are changes? I miss something?
>
> # btrfs fi df /; btrfs fi usage /;
> Data, single: total=1.41GiB, used=704.47MiB
> System, single: total=32.00MiB, used=16.00KiB
> Metadata, single: total=256.00MiB, used=54.30MiB
> GlobalReserve, single: total=32.00MiB, used=0.00B
> Overall:
>    Device size:                   4.00GiB
>    Device allocated:              1.69GiB
>    Device unallocated:            2.31GiB
>    Device missing:                  0.00B
>    Used:                        758.79MiB
>    Free (estimated):              3.03GiB      (min: 3.03GiB)
>    Data ratio:                       1.00
>    Metadata ratio:                   1.00
>    Global reserve:               32.00MiB      (used: 0.00B)
>
> Data,single: Size:1.41GiB, Used:704.47MiB
>   /dev/sda1       1.41GiB
>
> Metadata,single: Size:256.00MiB, Used:54.30MiB
>   /dev/sda1     256.00MiB
>
> System,single: Size:32.00MiB, Used:16.00KiB
>   /dev/sda1      32.00MiB
>
> Unallocated:
>   /dev/sda1       2.31GiB
>
> Thanks.
>

Re: True size of btrfs data chunk

[Duncan]

Austin S. Hemmelgarn posted on Tue, 29 Nov 2016 09:58:50 -0500 as
excerpted:

> On 2016-11-29 09:32, Timofey Titovets wrote:
>> Hi, as wiki say https://btrfs.wiki.kernel.org/index.php/Glossary:

Bad link.  Without the terminating colon it works, however.

https://btrfs.wiki.kernel.org/index.php/Glossary

>> A part of a block group. Chunks are either 1 GiB in size (for data) or
>> 256 MiB (for metadata).

> This is only about the normal case.  Chunks are variable in size.  In
> most cases, data chunks will be 1GB and metadata 256MB.  They will
> however be smaller if there isn't enough space left for a full chunk,
> and will get larger as well once you get past a certain filesystem size
> (I don't remember the exact size, but I've seen people talking about big
> (double digit TB sized) filesystems with 5GB+ sized data chunks).

Yes.  The wiki is correct about the _nominal_ size, but it doesn't say 
"nominal", making the overall claim invalid.

If I had a wiki account I'd probably change it right now, but for 
personal reasons I don't fully understand myself, I seem to treat web 
pages, including wikis I could in theory edit, as read-only, even if the 
alternative is replying repeatedly to list threads such as this, vs. a 
single wiki edit.  [shrug]

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman