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watts3000

join:2002-01-21

software raid cpu usage

Guys my current file server is a Dell precision 390 which runs 5 Samsung 2TB drives in a raid 5 along with a perc 5i controller. I run Windows server 2008 R2 I'm wanting to retire my perc 5i the card puts off a ton of heat in favor of an HBA style controller where I will just pass the drives through to the OS as JBODS and use sofware raid. I would be running Centos if I rebuild our file server I've heard software raid uses a lit of cpu this box is an intel core2duo 1.86 with 4 gigs of ram do you guys think I have enough cpu to run sofware raid?


shdesigns
Powered By Infinite Improbabilty Drive
Premium
join:2000-12-01
Stone Mountain, GA
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I ran software RAID on my dual CPU PIII with no problems and 512meg RAM. I did change it to mirrored later.

It is not the CPU overhead but the added time to write to the parity sectors. A hardware RAID card can do that in parallel while the CPU needs to do it as a separate step.


clarknova

join:2010-02-23
Grande Prairie, AB
kudos:7
reply to watts3000
I have a NAS with four drives running as two RAID1 pairs in software, all on an Atom 330. The CPU is not breaking a sweat serving files over gigabit. Disk IO and network are the bottlenecks here.
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db

watts3000

join:2002-01-21
reply to watts3000
How have you determined that the bottle neck is the network? I know some people use nic teaming on there home file servers.


DeHackEd
Bill Ate Tux's Rocket

join:2000-12-07

1 recommendation

reply to watts3000
I think you're worrying too much. On such good hardware (yes, a core 2 duo is good) the RAID calculation won't be what kills you.

Also note that except when you have a failed drive, reading from RAID incurs nearly no CPU penalty since it's just sector number mapping. Writes, verifies and rebuilds do cost CPU time but RAID-5 is simple enough to not be worth worrying about.

What you want to do is be diligent in RAID checking, which luckily CentOS does by default every Sunday morning.
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That's odd...