Date: Sat, 18 Sep 1999 22:57:12 -0300 (ADT) From: The Hermit Hacker <scrappy@hub.org> To: Greg Lehey <grog@lemis.com> Cc: freebsd-questions@freebsd.org Subject: Re: mirroring one drive to another...vinum? Message-ID: <Pine.BSF.4.10.9909182247240.27097-100000@thelab.hub.org> In-Reply-To: <19990919110524.U55065@freebie.lemis.com>
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On Sun, 19 Sep 1999, Greg Lehey wrote:
> > what I want to do is mirror da0s1a->da1s1a, da0s1?->da0s1?,
> > etc...which, to my understanding, isn't even RAID-5, but RAID-1...
>
> Precisely. What kind of plex do you want in the mirror? Normally you
> wouldn't use RAID-5.
You lose me here...if I try to equate this to what I know, is a 'plex' the
sam as what Solaris/Disksuite calls a 'metadevice'?
Basically, under solaris/Disksuite, if I mirror /dev/dsk/c0t1d0s1 with
/dev/dsk/c1t1d0s1, I get /dev/md/dsk/d0...and its /dev/md/dsk/d0 that I
mount.
Under vinum, if I mirror /dev/da0s1a to /dev/da1s1a, I would get a 'plex'?
> > Basically, I want to mirror my system disk to a second drive on
> > the same size/make, so that if one dies, my whole system doesn't go
> > poof...
>
> Sounds like you need concatenated plexes.
Huh? Again, its your terminology that is probably what is throwing me,
but if I concatenate /dev/da0s1a to /dev/da1s1a, the end result is the sum
of the two drives, where /dev/da0s1a would fill up first, then da1s1a ...
concatenating is what I'd use with hard drives of a different size to
combine them (ie. ccd). If I stripe, then I do the same, but both drives
have to be the same size (or, rather, both partitions have to be) and I
get a performance increase since it writes alittle to each drive to
spread the load...
Again, my knowledge is based on how Disksuite talks about things..
> Then gain, I just checked 'man 4 vinum', and it also states it
> requires a minimum of 3...
>
> I don't see anything like that in vinum(4).
o RAID-5 plexes require at least three equal-sized subdisks.
> > Please note that my use of RAID=1 is from the Solaris/DiskSuite
> > environment...I'm new to it with FreeBSD/Vinum :(
>
> You've been talking about RAID-5, which is not the same as RAID-1. To
> quote the web page, which is correct:
>
> Vinum imposes an additional, trivial restriction: a striped plex
> must have at least two subdisks, since otherwise it is
> indistinguishable from a concatenated plex.
>
> Vinum enforces a minimum of three subdisks for a RAID-5 plex,
> since any smaller number would not make any sense.
>
> There is no such restriction for concatenated plexes.
Okay, we've got to be talking the same thing in two different languges :(
How does this work? If I'm understanding you correctly...if I want to do
this, I have to "convert" /dev/da0s1a and /dev/da1s1a to "concatenated
plexes" consisting of one subdisk each, and then I RAID-1 the two plexes
together?
Or, in Disksuite-speak...convert the two subdisks to a metadevice
considering of one device and then link'ng the two together as RAID-1...
If this is correct...is there instructions/examples on how to do thsi with
the system disk? ie. /?
Thanks...
Marc G. Fournier ICQ#7615664 IRC Nick: Scrappy
Systems Administrator @ hub.org
primary: scrappy@hub.org secondary: scrappy@{freebsd|postgresql}.org
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