Re: HAMMER update 10-Feb-2008

[Bill Hacker <wbh@xxxxxxxxxxxxx>]

Matthew Dillon wrote:
>     HAMMER is really shaping up now. Here's what works now:

*snip*

>     I have already run some tests with regards to the blockmap allocation
>     model and it looks very good.   What I did was implement an array of
>     blockmap entry structures rather then just an array of pointers to the
>     actual physical big-blocks.  The blockmap entry structure not only has
>     a pointer to the underlying physical big-block, it also has a
>     bytes_free field which specifies how many bytes in the underlying
>     big-block are free.
>
>     This is the only tracking done by the blockmap.  It does not actually
>     try to track WHERE in the big-block the free areas are... figuring
>     that out will be up to the cleaning code.  What this gives us is the
>     following:
>
>     * Extremely fast freeing of on-disk storage elements.  The target
>       physical block doesn't have to be read or written, only the governing
>       blockmap entry.  With 8MB big-blocks and 32-byte blockmap entries one
>       16K buffer can track 4GB worth of underlying storage, which means
>       that freeing large amounts of sparse information does not cause the
>       disk to seek all over the place.

*snip*

Struggling today with a situation wherein 82 Giga-bytes of data were 
moved into an IMAP trash folder on UFS2, outrunning inodes, names et al 
before disk space (plenty of that left) and a cleanup that gets:

/bin/rm: Argument list too long

Unless I script it into manageable chunks....

If HAMMER fs has a better, even mechanism - even a rahter BFBI one, to 
handle that sort of need for massive deletions, it will make a convert here.

Bill