[WBEL-users] Software raid and User Mode Linux CD burning on WBEL

[James Knowles]

> Along these lines, does anyone know how much overhead Software RAID 
> introduces?


I'd like to counter the idea that soft RAID introduces a lot of 
overhead. I've been using it since it was first introduced into the kernel.

It doesn't really add much overhead, even on the pokey 233MHz server 
(soft RAID-5) that's been in service since 233MHz Pentrium-II was the 
rage of the day. For old machines I expect a 5% increase in CPU overhead 
with IDE, lower with SCSI. The worst I ever saw was 15% CPU increase 
under bitter load and IDE drives.

Of course, on modern multi-GHz processors, soft RAID hardly impacts the 
machine.

Since soft RAID was stabilized in the kernel years ago, I've never seen 
it put data at risk, including the harshest loads.

Since hard drives have become cheap, we've always run our workstations 
with soft RAID-1, which has saved our bacon more than once over the 
years. It costs more to slap in an extra hard drive, but it's cheaper 
than what it does to a business on the rare day when a HD decides to 
roll over and die. The worst case is when the HD takes out swap, the 
kernel panics, and we have to yank the cable to the offending drive. 
When there's a failure, we can wait until after hours to actually swap 
out the drive.

Anaconda has a nice interface for setting up soft RAID during install.

-- 
One-Day Introductory Course to Medieval Longsword
31 July 2004
http://www.thearma.org/events/utah_ntp10.htm