On Tue, 20 Nov 2007, Ross wrote:
>>> doing these writes now sounds like a
>>> lot of work. I'm guessing that needing two full-path
>>> updates to achieve this means you're talking about a
>>> much greater write penalty.
>>
>> Not all that much. Each full-path update is still
>> only a single write request to the disk, since all
>> the path blocks (again, possibly excepting the
>> superblock) are batch-written together, thus mostly
>> increasing only streaming bandwidth consumption.
>
... reformatted ...
> Ok, that took some thinking about. I'm pretty new to ZFS, so I've
> only just gotten my head around how CoW works, and I'm not used to
> thinking about files at this kind of level. I'd not considered that
Here's a couple of resources that'll help you get up to speed with ZFS
internals:
a) From the London OpenSolaris User Group (LOSUG) session, presented
by Jarod Nash, TSC Systems Engineer entitled: "ZFS: Under The Hood":
ZFS-UTH_3_v1.1_LOSUG.pdf
zfs_data_structures_for_single_file.pdf
also referred to as "ZFS Internals Lite".
and b) the ZFS on-disk Specification:
ondiskformat0822.pdf
> path blocks would be batch-written close together, but of course
> that makes sense.
>
> What I'd been thinking was that ordinarily files would get
> fragmented as they age, which would make these updates slower as
> blocks would be scattered over the disk, so a full-path update would
> take some time. I'd forgotten that the whole point of doing this is
> to prevent fragmentation...
>
> So a nice side effect of this approach is that if you use it, it
> makes itself more efficient :D
>
Regards,
Al Hopper Logical Approach Inc, Plano, TX. [EMAIL PROTECTED]
Voice: 972.379.2133 Fax: 972.379.2134 Timezone: US CDT
OpenSolaris Governing Board (OGB) Member - Apr 2005 to Mar 2007
http://www.opensolaris.org/os/community/ogb/ogb_2005-2007/
Graduate from "sugar-coating school"? Sorry - I never attended! :)
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