[mythtv-users] Reassemble RAID with mdadm [OT: RAID performance]

[Ian Clark]

On 16 March 2010 19:11, John Drescher <drescherjm at gmail.com> wrote:

> > Believe you can do a raid5 configuration with 3 drives.  However
> > generating the parity bit slows things down on the write.
> >
>
> That depends on tuning and how often the writes occur. The forced
> flushes with multiple streams work very much against performance.
> Tuning the stripe cache can reduce this problem but that risks
> corruption in the unlikely event that the system looses power or
> crashes.
>
>
Just out of interest (and slightly OT), how does linux cope speed wise when
your RAID5 array isn't (n+1) drives (where n is a power of 2)? I'm using
RAID5 on a NetBSD box and writing to a 4 drive RAID5 array is terrible,
which I think is due to disparity between the FS blocksize (which is a power
of 2) and the data per stripe (which isn't a power of two.) meaning lots of
read+write for every write to calc the extra parity.

Is this an issue on linux?

Cheers,

Ian
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