Re: Which is the maximum files size in BTRFS ? [was Re: btrfs: Probably the larger filesystem I will see for a long time]

[Goffredo Baroncelli <kreijack@libero.it>]

On 05/22/2012 07:17 PM, Goffredo Baroncelli wrote:
> Hi all,
> 
>>From the specification [1] the btrfs maximum file size limit should be
> 1<<64 bytes. However I was never able to create a file >= 1<<63 bytes.
> 
> 
> ghigo@venice:/mnt/old-btrfs/home/ghigo/gianfile$ ls -l giantfile2
> -rw-r--r-- 1 ghigo ghigo 9223372036854775807 May 22 18:55 giantfile2
> ghigo@venice:/mnt/old-btrfs/home/ghigo/gianfile$ ls -lh giantfile2
> -rw-r--r-- 1 ghigo ghigo 8.0E May 22 18:55 giantfile2
> ghigo@venice:/mnt/old-btrfs/home/ghigo/gianfile$ echo -n x >>giantfile2
> bash: echo: write error: File too large
> ghigo@venice:/mnt/old-btrfs/home/ghigo/gianfile$ python -c "print 1<<63"
> 9223372036854775808
> 
> Could be a kernel limit ?

Yes, it seems to be a kernel limit: the generic_file_llseek() function
check the lseek "offset" argument against superblock->s_maxbytes, which
is set to MAX_LFS_FILESIZE in btrfs. (see file fs/read_write.c and
fs/btrfs/super.c).
MAX_LFS_FILESIZE is defined in include/linux/fs.h as

  /* Page cache limit. The filesystems should put that into their
     s_maxbytes limits, otherwise bad things can happen in VM. */

  #if BITS_PER_LONG==32

  #define MAX_LFS_FILESIZE \
	(((u64)PAGE_CACHE_SIZE << (BITS_PER_LONG-1))-1)

  #elif BITS_PER_LONG==64

  #define MAX_LFS_FILESIZE 0x7fffffffffffffffUL

  #endif

Which means that in btrfs under linux there is a file size limit of 8EB
( 0x7fffffffffffffff +1 ).

Goffredo


> 
> Goffredo
> 
> [1] https://btrfs.wiki.kernel.org/index.php/Main_Page
> 
> P.S.
> I am asking about this un-useful question because I want to create a
> loop based btrfs filesystem on a file greater than 8E. But I was unable
> to create a such big file. I got success up to 8E-1
> 
> 
> 
> On 05/19/2012 05:03 AM, Christian Robert wrote:
>> Probably the larger filesystem I will ever see. Tryed 8 Exabytes but it
>> failed.
>>
>> [root@CentOS6-A:/root] # df
>> Filesystem                    1K-blocks      Used         Available 
>> Use%  Mounted
>> /dev/mapper/vg01-root          17915884  11533392           5513572  
>> 68%  /
>> /dev/sda1                        508745    140314            342831  
>> 30%  /boot
>> /dev/mapper/data_0             66993872   1644372          61994060   
>> 3%  /mnt/data_0
>> /dev/mapper/data_1     7881299347898368    508360  7881248224091896   
>> 1%  /mnt/data_1
>>
>> [root@CentOS6-A:/root] # df -h
>> Filesystem             Size  Used  Avail  Use%  Mounted
>> /dev/mapper/vg01-root   18G   11G   5.3G   68%  /
>> /dev/sda1              497M  138M   335M   30%  /boot
>> /dev/mapper/data_0      64G  1.6G    60G    3%  /mnt/data_0
>> /dev/mapper/data_1     7.0E  497M   7.0E    1%  /mnt/data_1
>>
>> [root@CentOS6-A:/root] # df -Th
>> Filesystem              Type  Size  Used  Avail  Use%
>> /dev/mapper/vg01-root   ext4   18G   11G   5.3G  68%
>> /dev/sda1               ext4  497M  138M   335M  30%
>> /dev/mapper/data_0      ext4   64G  1.6G    60G  3%
>> /dev/mapper/data_1     btrfs  7.0E  499M   7.0E  1%
>> [root@CentOS6-A:/root] #
>>
>>
>> [root@CentOS6-A:/root] # uname -rv
>> 3.4.0-rc7+ #23 SMP Wed May 16 20:20:47 EDT 2012
>>
>>
>> made with a dm-thin device sitting on a device pair composed of
>> (metadata 256Megs and data 23 Gigs)
>>
>> running on my laptop at home.
>>
>> yes, this is 7 Exabytes or 7,168 Petabytes or ( 7,340,032 Terabytes ) or
>> 7,516,192,768 Gigabytes.
>>
>>
>> please do not answer, it is just a statement of a fact at 3.4-rc7 (was
>> not working at 3.4-rc3 if I remember).
>>
>>
>> Xtian.
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