[mythtv-users] OT Hardware RAID 5 Recommendations

Brian Wood beww at beww.org
Tue Dec 12 19:26:15 UTC 2006

On Dec 12, 2006, at 12:15 PM, Yan Seiner wrote:

> George Galt wrote:
>> Brett:
>> Thanks, I'm looking for RAID5 which requires that a parity bit be set
>> across all of the disks.  This requires a fair bit of horsepower.
>> RAID1 is (if I remember correctly) simply a mirror, which would be a
>> waste of disk space.  On that point, I'm not sure if software RAID
>> does level 5.
> I've been doing software RAID5 for years.
> There's nothing to it; it barely loads up the CPU, even on  
> underpowered
> boxes.
> If you need to sync a new drive, that will take a while, but otherwise
> in operation it is transparent.

Hmmm... I haven't seen actual numbers but calculating the parity info  
does require *some* CPU.    The last time I compared them, systems  
with H/W RAID5 were significantly faster than ones using S/W RAID,  
but that was back when a 400Mhz. CPU was "fast".

One big advantage to software RAID is that the drives can be used on  
any Linux system without needing specific hardware, where hardware  
RAID depends on a specific card type being available. If a card type  
is discontinued you could potentially be in trouble, while with a S/W  
RAID system you should always be able to get your info in the event  
of H/W failure.

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