On 12/22/2010 11:49 AM, Tomas Ögren wrote:
On 22 December, 2010 - Jerry Kemp sent me these 1,0K bytes:
I have a coworker, who's primary expertise is in another flavor of Unix.
This coworker lists floating point operations as one of ZFS detriments.
I's not really sure what he means specifically, or where he got this
reference from.
Then maybe ask him first? Guilty until proven innocent isn't the regular
path...
In an effort to refute what I believe is an error or misunderstanding on
his part, I have spent time on Yahoo, Google, the ZFS section of
OpenSolaris.org, etc. I really haven't turned up much of anything that
would prove or disprove his comments. The one thing I haven't done is
to go through the ZFS source code, but its been years since I have done
any serious programming.
If someone from Oracle, or anyone on this mailing list could point me
towards any documentation, or give me a definitive word, I would sure
appreciate it. If there were floating point operations going on within
ZFS, at this point I am uncertain as to what they would be.
TIA for any comments,
Jerry
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/Tomas
So far as my understanding of the codebase goes (and, while I've read a
significant portion, I'm not really an expert here):
Assuming he means that ZFS has a weakness of heavy floating-point
calculation requirements (i.e using ZFS requires heavy FP usage), that's
wrong.
Like all normal filesystems, the "ordinary" operations are all integer,
load, and store. The ordinary work of caching, block allocation, and
fetching/writing is of course all integer-based. I can't imagine someone
writing a filesystem which does such operations using floating point.
A quick grep through the main ZFS sources doesn't find anything of type
"double" or "float".
I think he might be confused with what is happening on Checksums (which
is still all Integer, but looks/sounds "expensive"). Yes, ZFS is
considerably *more* compute intensive than other filesystems. However,
it's all Integer, and one of the base assumptions of ZFS is that modern
systems have lots of excess CPU cycles around, so stealing 5% for use
with ZFS won't impact performance much, and the added features of ZFS
more than make up for any CPU cycles lost.
--
Erik Trimble
Java System Support
Mailstop: usca22-123
Phone: x17195
Santa Clara, CA
Timezone: US/Pacific (GMT-0800)
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