Date: Mon, 7 Oct 1996 13:18:42 -0700 (PDT) From: Dmitry Kohmanyuk <dk@dog.farm.org> To: jrg@demon.net (James R Grinter) Cc: freebsd-hackers@freebsd.org Subject: Re: VPS mailing list, BSD interest? Message-ID: <199610072018.NAA24280@dog.farm.org>
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In article <E0v8PF4-0005Nt-00@chacal.noc.demon.net> you wrote:
> I (having been playing with IRIX 6.2 a lot recently) like IRIX's
> XFS/XLV setup. It's pretty similar to Sun's ODS/SDS, but you don't
> have to change md.conf files and reinit the metadevice when you
> move disks around controllers and change their ids.
> At boot time, an 'assemble' operation checks all disks on the
> system, and finds details of which logical volume they belong to,
> if any. (Someone's already said that they think it useful to be able
> to easily reconfigure your disks, and I concur - when you're dealing
> with large numbers of disks and large numbers of controllers you
> really don't want to have to be writing down numbers on pieces of
> paper.)
> Each logical volume has a name which is used when referring to the
> logical volume device (/dev/{r,}dsk/xlv/volumename), and consists
> of log, data, and real-time data sub-volumes. Each sub-volume
> consists of a number of volume elements (each being a disk partition),
> which can be concatenated or striped together. A sub-volume can
> contain up to 4 plexes (SGI's term for mirrors), each being up to
> 128 volume elements.
Sounds very familiar to what Tandem's System V volume daemon (vold)
uses... (have played with it for a while recently).
You divide your (physical) disks to subdisks, then merge several (or 1)
subdisk to a plex (allowing for a cross-device merge, and striping) and
then build a volume from one (or more) plexes (allowing for a redundancy,
crash-recovery, hot-swap (all pleaxes are maintained to be consistent,
and you can copy a volume to a new plex, then add this plex to volume).
Start-up determines which plexes are good enough to run a volume from,
selects one as active, then syncs all other plexes to match it.
All mappings are kept in a database. There are also some neat things
like log disks and volatile plexes allowing you to use some RAM-like
devices to cache drive's contents.
Hmm, maybe it's worth tarring a set of man pages and put them somewhere
on ftp to allow people interested to grasp the concept better?
> Of course, SGI have the advantage of not having tried to build the
> system around UFS/FFS, so you grow the filesystem whilst it is
> mounted (the instructions specifically say you *must* mount before
> growing!), and it's far better in crash situations.
> <URL:http://www.sgi.com/Technology/TechPubs/dynaweb_bin/0620/bin/nph-dynaweb.cgi/SGI_Admin/IA_DiskFiles/1.toc>;
--
Two months in the lab can save you two hours in the library.
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