Re: [PATCH] Btrfs-progs: btrfs file system size should be bigger then 256m

Re: [PATCH] Btrfs-progs: btrfs file system size should be bigger then 256m

[Tomasz Chmielewski]

> This has been bothering me for some time. Why does btrfs need to have a 
> disk greater then 256M? I could see a much smaller limit, say 16M but 
> why so much? The file system itself does not need that much space for 
> its own use.

In other words, 256M limit rather disqualifies btrfs as a filesystem 
i.e. for /boot, doesn't it?


-- 
Tomasz Chmielewski
http://wpkg.org

Re: [PATCH] Btrfs-progs: btrfs file system size should be bigger then 256m

[Tomasz Chmielewski]

Kaspar Schleiser schrieb:
> Hey,
> 
> Tomasz Chmielewski wrote:
>>> This has been bothering me for some time. Why does btrfs need to have 
>>> a disk greater then 256M? I could see a much smaller limit, say 16M 
>>> but why so much? The file system itself does not need that much space 
>>> for its own use.
>>
>> In other words, 256M limit rather disqualifies btrfs as a filesystem 
>> i.e. for /boot, doesn't it?
> When 1G is just 10c?

Maybe when talking about traditional HDDs.
Anything flash-based is still $2-$5 per 1G.

I have some SAN devices booting off 512MB or 1G builtin flash. Having 
256M for /boot there would not leave much more space for the operating 
system.

Why separate /boot? It's still needed for encrypted rootfs or more fancy 
partitioning (like / on LVM, at least until GRUB2 is stable and is 
shipped by major distros).


Seriously, what are the technical reasons that btrfs needs so much space 
for a minimal filesystem?

Just 2 MB is enough for mkfs.ext4 to create a valid filesystem.


Also, the patch seems to be incomplete - i.e. what will happen if we try 
to btrfs-convert a 50MB ext3 filesystem into btrfs?


-- 
Tomasz Chmielewski
http://wpkg.org

Re: [PATCH] Btrfs-progs: btrfs file system size should be bigger then 256m

[Chris Mason]

On Mon, 2009-01-05 at 16:49 +0100, Tomasz Chmielewski wrote:
> Kaspar Schleiser schrieb:
> > Hey,
> > 
> > Tomasz Chmielewski wrote:
> >>> This has been bothering me for some time. Why does btrfs need to have 
> >>> a disk greater then 256M? I could see a much smaller limit, say 16M 
> >>> but why so much? The file system itself does not need that much space 
> >>> for its own use.
> >>
> >> In other words, 256M limit rather disqualifies btrfs as a filesystem 
> >> i.e. for /boot, doesn't it?
> > When 1G is just 10c?
> 
> Maybe when talking about traditional HDDs.
> Anything flash-based is still $2-$5 per 1G.
> 
> I have some SAN devices booting off 512MB or 1G builtin flash. Having 
> 256M for /boot there would not leave much more space for the operating 
> system.
> 
> Why separate /boot? It's still needed for encrypted rootfs or more fancy 
> partitioning (like / on LVM, at least until GRUB2 is stable and is 
> shipped by major distros).
> 
> 
> Seriously, what are the technical reasons that btrfs needs so much space 
> for a minimal filesystem?

This is mostly to help prevent crashes on enospc.  As we fixup the
kernel code, the 256MB limit will go away.

-chris

[PATCH] Btrfs-progs: btrfs file system size should be bigger then 256m

[Shen Feng]

According to btrfs_prepare_device, btrfs file sysstem size
should be bigger then 256m.

If mkfs.btrfs specifies the file system size samaller then
that, mkfs.btrfs should report error.

Signed-off-by: Shen Feng <shen@cn.fujitsu.com>
---
 mkfs.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/mkfs.c b/mkfs.c
index be93aaa..447e8d7 100644
--- a/mkfs.c
+++ b/mkfs.c
@@ -377,6 +377,10 @@ int main(int ac, char **av)
 				break;
 			case 'b':
 				block_count = parse_size(optarg);
+				if (block_count < 256*1024*1024) {
+					fprintf(stderr, "File system size is too small\n");
+					exit(1);
+				}
 				zero_end = 0;
 				break;
 			default:
-- 
1.6.0.6

Re: [PATCH] Btrfs-progs: btrfs file system size should be bigger then 256m

[Lee Trager]

This has been bothering me for some time. Why does btrfs need to have a 
disk greater then 256M? I could see a much smaller limit, say 16M but 
why so much? The file system itself does not need that much space for 
its own use.

Thanks,

Lee

Shen Feng wrote:
> According to btrfs_prepare_device, btrfs file sysstem size
> should be bigger then 256m.
>
> If mkfs.btrfs specifies the file system size samaller then
> that, mkfs.btrfs should report error.
>
> Signed-off-by: Shen Feng <shen@cn.fujitsu.com>
> ---
>  mkfs.c |    4 ++++
>  1 files changed, 4 insertions(+), 0 deletions(-)
>
> diff --git a/mkfs.c b/mkfs.c
> index be93aaa..447e8d7 100644
> --- a/mkfs.c
> +++ b/mkfs.c
> @@ -377,6 +377,10 @@ int main(int ac, char **av)
>  				break;
>  			case 'b':
>  				block_count = parse_size(optarg);
> +				if (block_count < 256*1024*1024) {
> +					fprintf(stderr, "File system size is too small\n");
> +					exit(1);
> +				}
>  				zero_end = 0;
>  				break;
>  			default:
>   

Re: [PATCH] Btrfs-progs: btrfs file system size should be bigger then 256m

[Shen Feng]

My test shows that at least 100M is needed for a btrfs partition.

on 12/31/2008 03:41 PM, Lee Trager wrote:
> This has been bothering me for some time. Why does btrfs need to have a
> disk greater then 256M? I could see a much smaller limit, say 16M but
> why so much? The file system itself does not need that much space for
> its own use.
> 
> Thanks,
> 
> Lee
> 
> Shen Feng wrote:
>> According to btrfs_prepare_device, btrfs file sysstem size
>> should be bigger then 256m.
>>
>> If mkfs.btrfs specifies the file system size samaller then
>> that, mkfs.btrfs should report error.
>>
>> Signed-off-by: Shen Feng <shen@cn.fujitsu.com>
>> ---
>>  mkfs.c |    4 ++++
>>  1 files changed, 4 insertions(+), 0 deletions(-)
>>
>> diff --git a/mkfs.c b/mkfs.c
>> index be93aaa..447e8d7 100644
>> --- a/mkfs.c
>> +++ b/mkfs.c
>> @@ -377,6 +377,10 @@ int main(int ac, char **av)
>>                  break;
>>              case 'b':
>>                  block_count = parse_size(optarg);
>> +                if (block_count < 256*1024*1024) {
>> +                    fprintf(stderr, "File system size is too small\n");
>> +                    exit(1);
>> +                }
>>                  zero_end = 0;
>>                  break;
>>              default:
>>   
> 
> -- 
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> 
> 

-- 
Best Regards,
--------------------------------------------------
Shen Feng
Development Dept.I
Nanjing Fujitsu Nanda Software Tech. Co., Ltd.(FNST)
8/F., Civil Defense Building, No.189 Guangzhou Road,
Nanjing, 210029, China
PHONE: +86-25-86630566-950
COINS: 79955-950
FAX: +86-25-83317685
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Re: [PATCH] Btrfs-progs: btrfs file system size should be bigger then 256m

[Zach Brown]

> +				if (block_count < 256*1024*1024) {
> +					fprintf(stderr, "File system size is too small\n");
> +					exit(1);
> +				}

And please, if you could, include both the size that is too small and
the size that is required in the message.

- z

Re: [PATCH] Btrfs-progs: btrfs file system size should be bigger then 256m

[Shen Feng]

on 01/01/2009 01:49 AM, Zach Brown wrote:
>> +				if (block_count < 256*1024*1024) {
>> +					fprintf(stderr, "File system size is too small\n");
>> +					exit(1);
>> +				}
> 
> And please, if you could, include both the size that is too small and
> the size that is required in the message.
> 

Thanks. I updated the patch.

Signed-off-by: Shen Feng <shen@cn.fujitsu.com>
---
 mkfs.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/mkfs.c b/mkfs.c
index be93aaa..cb21db6 100644
--- a/mkfs.c
+++ b/mkfs.c
@@ -377,6 +377,13 @@ int main(int ac, char **av)
 				break;
 			case 'b':
 				block_count = parse_size(optarg);
+				if (block_count < 256*1024*1024) {
+					fprintf(stderr, "File system size "
+						"%llu bytes is too small, "
+						"256M is required at least\n",
+						block_count);
+					exit(1);
+				}
 				zero_end = 0;
 				break;
 			default: