Getting started the hard way with RAID

Marius Gedminas marius at pov.lt
Sun Dec 4 00:08:29 UTC 2011


On Sat, Dec 03, 2011 at 11:26:44AM -0800, Kevin O'Gorman wrote:
> On Sat, Dec 3, 2011 at 9:46 AM, Kevin O'Gorman <kogorman at gmail.com> wrote:
> > I just worked up the courage to try dmraid.  So far, I've
> > only tried discovery, but it's promising:
> > root at treat:~# dmraid -r
> > /dev/sdd: ddf1, ".ddf1_disks", GROUP, ok, 976494592 sectors, data@ 0
> > /dev/sdb: ddf1, ".ddf1_disks", GROUP, ok, 976494592 sectors, data@ 0

Neat!  But why isn't 3ware mentioned in dmraid's README then?  Google
gives me the impression 3ware is a big name in the hardware RAID
business.

> > That's exactly the two disks that had the mirror halves, and the size
> > is convincing.  I don't understand everything it's showing, and I
> > haven't had the courage to actually turn it on yet....
> 
> With a little more courage, I tried and failed.
> 
>   root at treat:~/work# dmraid -r
>   /dev/sdd: ddf1, ".ddf1_disks", GROUP, ok, 976494592 sectors, data@ 0
>   /dev/sdb: ddf1, ".ddf1_disks", GROUP, ok, 976494592 sectors, data@ 0
>   root at treat:~/work# dmraid -ay
>   ERROR: ddf1: wrong # of devices in RAID set "ddf1_SimpleVol" [2/1] on /dev/sdd
>   ERROR: ddf1: wrong # of devices in RAID set "ddf1_SimpleVol" [2/1] on /dev/sdb
>   RAID set "ddf1_SimpleVol" was not activated

Oh :(

> In fact, I find the man page for dmraid very confusing and have been
> unable to get any other commands to even try...
> 
> For instance, to display data "dmraid -r" works and so does "dmraid
> -rc", but further embellishments fail.
> -- root at treat:~/work# dmraid -r --display_columns=ser
> *ERR*
> *ERR*

Now I've never used dmraid in my life, but seeing the extreme weirdness
of the command syntax (why --display_columns and not
--display-columns?), and given that the syntax in the man page

  [-c|--display_columns][FIELD[,FIELD...]]...

so maybe  you're not supposed to use a '=' sign?  There are examples
that use -c and don't separate it from the field list, e.g.

  dmraid -r --sep : -cpath:size

> And so it goes.  I'll be looking for other documentation as soon as I
> finish figuring out ufw enough so that I can have a firewall and a web
> page at the same time.  It appears to me that the man pages for the
> more advanced stuff were not meant for human consumption...

The dmraid manual page is, I think, the worst manual page I've ever
seen.

It could be worse: at least it exists...

Marius Gedminas
-- 
... Another nationwide organization's computer system crashed twice in less
than a year. The cause of each crash was a computer virus....
                -- Paul Mungo, Bryan Glough  _Approaching_Zero_
(in 1986 computer crashes were something out of the ordinary.  Win95 anyone?)
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