cvs commit: src MAINTAINERS

Poul-Henning Kamp phk at
Tue Aug 17 06:44:07 PDT 2004

In message <20040817132740.GA32139 at>, Wilko Bulte writes:

>RAID-3 IIRC uses a dedicated parity disk, and small stripes.  I don't think
>it must be bytelevel striping.  Just small enough stripes that all disks
>contribute to every I/O

RAID3 differs from RAID5 in that you always access the entire stripe
and never have R/M/W cycles.

Typically the problem is that by doing so you get a RAID3 sectorsize
which is the sum of all non-parity sectors, a 4+1 will give you
4 x 512 = 2048 and 8 + 3 will give you 4k.

Since a lot of filesystems/OS/hardware can only work with 512 byte
sectors, people have hacked around this in various ways and eventually
given up on RAID3.

UFS/FFS works fine with 1k, 2k, 4k and larger sectorsizes and so
RAID3 is a great idea for FreeBSD, and I'd rather use RAID3 than
RAID5 myself.

Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

More information about the cvs-all mailing list