when ufs is 99% full, current seems to limit creat to 28672 bytes

[Shane Ambler]

On 25/12/2016 20:41, Gary Jennejohn wrote:
> On Sun, 25 Dec 2016 04:30:49 +0100
> "Julian H. Stacey" <jhs at berklix.com> wrote:
>
>> A puzzle below, that I think I've solved, but comments welcome:
>> When ufs is 99% full, current limits creat to 28672 bytes.
>>

>> Produces loads of little files of size 28672 bytes = 0x7000
>>
>> A foreground fsck of FS shows no errors.  No ZFS in use.  Where
>> does all the extra space come from ?  Why does it keep allowing
>> more little files ?  But not files bigger than 7K ?

>
> I suspect this ia a result of how UFS is designed.  Did you use the
> standard options for block and fragment size?  How about inodes?
>

Been a while since I looked into filesystem specs but as I recall -

My guess is free block fragmentation - I believe on UFS each file is
kept in a continuous strip of blocks on disk. If blocks are 8K and the
system is unable to find more than one free block between existing files
it would prevent a new file over 8k being created, even though there may
be MB of free blocks available throughout the filesystem. At a certain
fill factor moving files to create enough free space becomes too costly.

There is also fragmentation, I understand that multiple (or just two)
small files can be stored in one block, so a 3k file can be added to a
block that already has a 3k file on it, but it may be unable to find
space to create a new 12k file.


-- 
FreeBSD - the place to B...Storing Data

Shane Ambler