[linux-elitists] Broken promises (was: The desktop in your pocket)

Andrew akohlsmith-le@benshaw.com
Tue Jan 27 18:41:36 PST 2004


> But me too. Promise's RAID drivers are mostly implemented in software,
> which explains why Linux software RAID seems faster here too. Since
> there's more people using Linux SW RAID than Promise's dodgy drivers,
> its more stable code too and easier to recover with.

I actually did some real-life testing with a DPT 2044U (UW2 HW RAID) card, 
using their hardware, i960-enhanced RAID1 with Linux's software RAID1.  
Linux beat it out _soundly_ -- I ran the test several times to make sure 
that I wasn't doing something really wrong but linux MD RAID came up on top 
every time.

It's not a really scientific test but I've found that if you aren't throwing 
enough processor at a system so that the trivial software overhead of RAID1 
is noticeable, you're speccing your systems far too closely.

RAID5 is a different story; the amount of overhead in calculating the parity 
(yeah I know XOR) and writing *different* data to different disks is (IMO) 
significantly higher than straight-out mirroring.

Regards,
Andrew



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