[nycbug-talk] FreeBSD software RAID?

[Dan Langille]

On 7 Mar 2007 at 23:04, Andy Michaels wrote:

> On Mar 7, 2007, at 10:46 PM, Steven Kreuzer wrote:
> 
> >
> > On Mar 7, 2007, at 9:48 PM, Miles Nordin wrote:
> >
> >>>>>>> "jv" == Jonathan Vanasco <nycbug-list at 2xlp.com> writes:
> >>
> >>     jv> Is there a preferred software raid on FreeBSD ?
> >>
> >> I think the RAID3 software RAID is theoretically more sound than the
> >> RAID5.  I don't have direct experience, but please don't be fooled
> >> into the crappier implementation by the larger number.
> >
> > Cut n Paste from wikipedia because it sums it up better then I can:
> >
> > RAID 3 uses byte-level striping with a dedicated parity disk. RAID 3
> > is very rare in practice. One of the side-effects of RAID 3 is that
> > it generally cannot service multiple requests simultaneously.
> > This comes about because any single block of data will, by
> > definition, be spread across all members of the set and will reside
> > in the same location. So, any I/O operation requires activity on
> > every disk.
> >
> > I have never used it at all, but I would stay the hell away from RAID
> > 3, both hardware and software implementations
> >
> > SK
> >
> So we have Miles saying (I think) that the RAID3 implementation in 
> FreeBSD is better than the RAID5 implementation, then Steven saying 
> that RAID3 is the redheaded stepchild of disk arrays.

Andy: The discussions you read about RAID5 and RAID3 where not based 
on the "FreeBSD implementation".  They were about RAID in general.  
They were discussing the pros and cons that that particular RAID 
configuration.  They were *not* talking about any particular 
implementation of RAID.  It is an important point.

Reading this might help understand the various RAID configurations:

   http://en.wikipedia.org/wiki/Redundant_array_of_independent_disks

> I'm beginning to think that software RAID on FreeBSD isn't worth the
> hassle and a modest investment in a supported RAID card is in order. 
> Is this the real recommendation? 

Nobody said that in what you quoted.  They were steering you away 
from RAID-3 and from RAID-5.  Personally, I recommend RAID-1 
(mirroring, minimum of 2 disks) or RAID-10 (mirroring and striping, 
minimum of 4 disks).

I have a few servers using RAID: RAID-1, RAID-10, and RAID-5.  

I have nothing running software RAID, but that it not for any 
particular reason.  Certainly, for a simple RAID-1, there's not much 
to setting it up on FreeBSD.  See what Dru did:

  http://www.onlamp.com/pub/a/bsd/2005/11/10/FreeBSD_Basics.html

-- 
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my resume: http://www.freebsddiary.org/dan_langille.php
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