Re: HAMMER update 19-June-2008 (56C) (HEADS UP - MEDIA CHANGED)

["Dan M" <strangepics@xxxxxxxxx>]

On Fri, Jun 20, 2008 at 12:57 PM, Matthew Dillon
<dillon@apollo.backplane.com> wrote:
>        * MTime will be updated semi-synchronously and will be CRCd.
>          (It will be fully synchronous from the point of view of
>          anyone using the filesystem, of course).  UNDO records will
>          be generated but new inode_data records will not have to be
>          created.  The mtime will be updated in-place.

Pardon my ignorance if I am missing something, I haven't looked much
into HAMMER yet.

Will the FS have the same atomic update features that UFS has? Meaning
fsync(2) returns only when all directory entries are safely on the
disk (whether it's with softupdate-type ordering or journaling). It's
important for mail servers and such so they don't lose messages at the
time of powerfail/crash. If you dig around mailing lists, you'll find
interesting stories how people who ran their FS mounted async (the
default Linux EXT2/3 mount) for mail servers (and AFAIK at least on
Linux in that case fsync returns early - not atomic, so software
written with BSD behavior in mind wasn't safe to run without patching)
found some of the messages in lost+found.

Also will there be a feature to grow/and or shrink the FS live without
having to unmount? I can do this right now with XFS and LVM on Linux
(grow, but not shrink), and its working amazingly well and very
quickly to boot.

Thanks.

-- 
Dan