[nycbug-talk] mdconfig file backed disks

[Isaac Levy]

Hey Mike, All,

I just wanted to give a shout out to list, to see if anyone else had  
seen noticable slowdowns using file backed disks on FreeBSD (Disk  
Images).

A primer on File and Memory backed disks can be found here:
http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/disks- 
virtual.html
(it's more or less what I'm going from for my disks).

Writes seem about twice as slow as they are from straight disk (yuck).

--
As an aside, when speaking to Mike about this long ago, he noted that  
non SMP machines didn't have the same level of performance hit, but  
I'm wondering by how much?  (I'm also wondering if this wasn't  
improved greatly with the last CURRENT, in mid-December).

Just wondering if anyone else had experiences tuning File-Backed  
disks here.

Rocket-
.ike



Using the utility Bonnie, I got the following output:

http://www.textuality.com/bonnie/advice.html

An SATA RAID5 volume:
               -------Sequential Output-------- ---Sequential Input--  
--Random--
               -Per Char- --Block--- -Rewrite-- -Per Char- --Block---  
--Seeks---
Machine    MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec % 
CPU  /sec %CPU
adaptecR  100 13971 11.4 10194  2.0 17029  2.1 116317 99.8 2509557  
99.9 91114.1 98.9


A file-backed disk which resides on the above SATA volume:
               -------Sequential Output-------- ---Sequential Input--  
--Random--
               -Per Char- --Block--- -Rewrite-- -Per Char- --Block---  
--Seeks---
Machine    MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec % 
CPU  /sec %CPU
fileDisk  100  4888  3.9  4864  0.8  5807  1.1 109823 99.6 2497500  
99.7 90007.0 98.8


Note: Output seems 2-3 times slower with the file backed virtual  
disks...