[clue-talk] BAARF - Battle Against Any Raid Five (er, Four, er Free.)

[Angelo Bertolli]

On Fri, October 19, 2007 10:50 pm, Jed S. Baer wrote:
> On Fri, 19 Oct 2007 19:44:28 -0600
> Nate Duehr wrote:
>
>> Good technical detail about why RAID-5 isn't always (in fact rarely)
>> the correct technical solution for disk redundancy...
>>
>> http://www.miracleas.com/BAARF/BAARF2.html
>
> I remember reading Cary Millsap's articles way back when. But I have to
> wonder, if RAID5 is so bad, why is it still so popular?


Because... it works.  I've started reading the site, and maybe it's
supposed to be satirical.  Actually we use RAID6 where I work when we can,
and RAID5 when we cannot.  Although RAID6 isn't one of the original
standards, it's become a de-facto standandard meaning that you essentially
have double parity using Solomon codes.

Now, keep in mind when you're reading these arguments that you're not
SUPPOSED to take all of your drives and make one huge RAID5.  What's the
point of only having the capability of failing only ONE drive?  But like I
said:  it works because people determine how many drives can at one time
can fail and build their RAID5's accordingly.  It's really unnecessary to
make everything a RAID1:  one out of two drives do NOT fail before they
can be replaced.

Also, when you get into RAID hardware, you can set up a drive to be a
global spare.  Therefore, even with RAID5 you can be sure that if no one
is there to replace a drive, you'll have some time before it's time to get
another one.

We also do use RAID1, but that's only in the case on individual machines
where we don't need huge amounts of storage.  The articles on the site
seem to make a case for RAID5 for Oracle databases.  There may be a case
for that, but the idea that everyone should just be using RAID1 instead of
RAID5 is pretty silly.

Angelo