Date: Tue, 11 Aug 1998 17:21:57 -0600 (MDT) From: Scott Leutenegger <leut@cs.du.edu> To: freebsd-questions@FreeBSD.ORG Subject: raw disk question Message-ID: <Pine.SOL.3.96.980811172046.20645A-100000@chocolate>
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Hi,
Want to help convert a solaris user to FreeBSD?
Question: Does FreeBSD support raw disks access?
i.e. a read/write to/from disk does NOT access
the file cache in memory, but rather 100% of the
accesses go-to/come-from disk.
If so, how do I create the raw disk partition?
Note: I am trying to decide whether to install solarix x86 or
FreeBSD on a cluster of PCs to build a parallel database
application (parallel multi-dimensional indexing)
I know solaris x86 supports this, but have been lead to believe
FreeBSD will be faster, easier to install/maintain, and
comes loaded with most of the software (gcc/g++/sockets/perl) I need.
(please correct me if I am wrong)
Further Explanation: (not really relevant, explains why raw disk access desired)
Our project has been developed on Sun's running solaris,
but due to the cost tradeoff we bought 10 PCs to build a cluster.
We do our own buffer pool (memory) caching.
When a read/write is exectued I want the data
to come/go straight from/to disk, ignoring any file system caching.
Bye the way, no, I do not think I can implement a better caching policy.
Rather, I need this functionality to enable measurements
for the number of disk I/O for various memory sizes. The applications
do run faster using a file rather than raw I/O (since you get
many buffer hits), but I need the flexibility and predictablility
of a raw disk.
If you are really curious, check out the methodology section of:
"The Effect of Buffering on the Performance of R-Trees" (postscript only)
at www.cs.du.edu/users/leut/pubs.html
Thanks,
---Scott
Professor Scott T. Leutenegger Phone: 303-871-2821
Math and CS Dept, Univ of Denver FAX: 303-871-3010
2360 S. Gaylord Street email: leut@cs.du.edu
Denver, CO 80208-0189 http://www.cs.du.edu/users/leut
Professor Scott T. Leutenegger Phone: 303-871-2821
Math and CS Dept, Univ of Denver FAX: 303-871-3010
2360 S. Gaylord Street email: leut@cs.du.edu
Denver, CO 80208-0189 http://www.cs.du.edu/users/leut
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