In article ,
gargoyle wrote:

> The OBSD 3.7 ccd man page says it supports mirroring. What
> advantages/disadvantages does it have in comparison to raidframe
> in a raid1 configuration?
>
> Which is more reliable/robust?
>
> Which uses less OS resources?
>
> Which is easier to recover after a hard system crash or disk failure?
>
> Can ccd mirror the / partition? (raidframe can but I think you can't
> boot directly onto the raid, so a separate boot partition is needed)
>
> The ccd driver is already included in GENERIC, but raidframe is not and
> requires a bit more work to setup. Is it worth it, or is ccd just as
> good?
>
> Which would you use to protect your data?...

RAID frame supports more than just striping and mirroring.
Personally I use RAID level 5 and with a bit of work you can use that
for / and the rest ...

Not used ccd as until your post I wasn't aware it could do mirroring.
also to use mirroring I'd need an additional disk (I have 3 x 200GB disk
and that gives me 400GB of protected storage in raid 5 - for mirroring
I'd need 4 disks).

On 2005-05-19, Ryoko wrote:
> RAID frame supports more than just striping and mirroring.
> Personally I use RAID level 5 and with a bit of work you can use that
> for / and the rest ...

That's true, but I'm only interested in RAID-1. It's more expensive,
but easier to deal with and that justifies the additional cost for me.

It should also be less resource-hungry than RAID-5 since there is no
XOR overhead, but I don't know if that makes much difference or not.

> Not used ccd as until your post I wasn't aware it could do mirroring.
> also to use mirroring I'd need an additional disk (I have 3 x 200GB disk
> and that gives me 400GB of protected storage in raid 5 - for mirroring
> I'd need 4 disks).

Yup, it cost more. OTOH, you could lose two disks and still have a
working system (unless both disks of the same mirror die!) Of course,
you could make that 4th disk a hot spare for your RAID-5 and get more
reliability that way too.

But I like RAID-1 for the simplicity, and also because some of my
machines simply don't have room or power for more than two disks.
Hence, I'm using raidframe in raid1 mode now, but I'm wondering if
there's any incentive to go with ccd mirror instead...

gargoyle writes:

> It should also be less resource-hungry than RAID-5 since there is no
> XOR overhead, but I don't know if that makes much difference or not.

The disk I/O is probably more likely to affect performance, not the
XOR calculation (especially on today's CPU). The following paper
describes the I/O characteristics of various RAID schemes:

http://citeseer.ist.psu.edu/chen89evaluation.html

The following two may also be of some interest:

http://citeseer.ist.psu.edu/chen90maximizing.html
http://citeseer.ist.psu.edu/219910.html

> Yup, it cost more. OTOH, you could lose two disks and still have a
> working system (unless both disks of the same mirror die!) Of
> course, you could make that 4th disk a hot spare for your RAID-5 and
> get more reliability that way too.

Depending on your I/O characteristics and speed needs, RAID 0+1 may be
another idea.

--
David Magda
Because the innovator has for enemies all those who have done well under
the old conditions, and lukewarm defenders in those who may do well
under the new. -- Niccolo Machiavelli, _The Prince_, Chapter VI