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/freebsd-11-stable/sbin/geom/class/raid3/
H A Dgeom_raid3.cdiff 134124 Sat Aug 21 16:11:46 MDT 2004 pjd Implement new reading algorithm, which will use parity component for reading
as well, even if device is in complete state.
I observe 40% of speed-up with this option for random read operations,
but slowdown for sequential reads.
Basically, without this option reading from a RAID3 device built from 5
components (c0-c4) looks like this:

Request no. Used components
1 c0+c1+c2+c3
2 c0+c1+c2+c3
3 c0+c1+c2+c3

With the new feature:

Request no. Used components
1 c0+c1+c2+c3
2 (c1^c2^c3^c4)+c1+c2+c3
3 c0+(c0^c2^c3^c4)+c2+c3
4 c0+c1+(c0^c1^c3^c4)+c3
5 c0+c1+c2+(c0^c1^c2^c4)
6 c0+c1+c2+c3
[...]
/freebsd-11-stable/sys/geom/raid3/
H A Dg_raid3.cdiff 134124 Sat Aug 21 16:11:46 MDT 2004 pjd Implement new reading algorithm, which will use parity component for reading
as well, even if device is in complete state.
I observe 40% of speed-up with this option for random read operations,
but slowdown for sequential reads.
Basically, without this option reading from a RAID3 device built from 5
components (c0-c4) looks like this:

Request no. Used components
1 c0+c1+c2+c3
2 c0+c1+c2+c3
3 c0+c1+c2+c3

With the new feature:

Request no. Used components
1 c0+c1+c2+c3
2 (c1^c2^c3^c4)+c1+c2+c3
3 c0+(c0^c2^c3^c4)+c2+c3
4 c0+c1+(c0^c1^c3^c4)+c3
5 c0+c1+c2+(c0^c1^c2^c4)
6 c0+c1+c2+c3
[...]

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