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Re: Questions about RAID 6

On Sunday 02 May 2010 06:00:38 Stan Hoeppner wrote:
> Good hardware RAID cards are really nice and give you some features you
> can't really get with md raid such as true "just yank the drive tray out"
> hot swap capability.  I've not tried it, but I've read that md raid doesn't
> like it when you just yank an active drive.  Fault LED drive, audible
> warnings, are also nice with HW RAID solutions.  The other main advantage
>  is performance.  Decent HW RAID is almost always faster than md raid,
>  sometimes by a factor of 5 or more depending on the disk count and RAID
>  level. Typically good HW RAID really trounces md raid performance at
>  levels such as 5, 6, 50, 60, basically anything requiring parity
>  calculations.

Speeds on my md-RAID devices were comparable to speeds with my Areca HW RAID 
controller (16-port, PCI-X/SATA, battery powered 128MB cache).  Number of 
drives varied from 5 to 10.  RAID levels 5 and 6 were both tested.

Read throughput for both were the expected (# drives - # parity drives) * 
single drive throughput.  Write throughput less than expected in both cases, 
but I can't recall the exact figures.

Both support "just yank the drive out" if the (rest of) the hardware supports 
hot plugging.  Alerting about failure is probably a bit better with a HW RAID 
controller, since it comes with visual and audible alarms.

It might be different when the system is under load, since the md-RAID depends 
on the host CPU and the HW RAID does not.  However, adding an additional 
generic CPU (to reduce load) is both more useful and often less expensive than 
buying a HW RAID controller that is only used for RAID operations.
> Sounds like you're more of a casual user who needs lots of protected disk
> space but not necessarily absolute blazing speed.  Linux RAID should be
>  fine.

I know I am.
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