[SATLUG] Software RAID

Walt DuBose dubose at texas.net
Fri May 23 08:17:00 CDT 2003


Chuck,

RAID 0 is mirroring of both drives.  If you lose one, the data is
mirrored on the other.

The advantage is that you don't have to shutdown if you lose a drive.
The disadvantage is that 2 drives only equals the diskspace of the
smallest drive.

At least that's what it is in hardware RAID.  I have no experience in
software RAID.

Walt

Chuck wrote:
> 
> Meant to ask you Borries, with a RAID 0 on just two drives -- you run
> the risk of loosing all data if just one drive fails, right?  I mean
> that with no parity partition (third,fourth,fifth,etc), there is no way
> to rebuild the data on the whole array if only one drive fails.
> 
> So, the only thing I can see you gaining out of using that RAID 0 is
> higher throughput.  But that would only occur if the two drives are on
> separate IDE channels.  If they were on the same channel, the chipset
> can only address one drive at a time and you would actually decrease
> throughput.
> 
> Am I right here Borries???
> 
> Chuck
> 
> On Mon, 2003-05-19 at 11:01, Borries Demeler wrote:
> > >
> > > Has anyone on the list implemented a software RAID in Linux???  I need
> > > to do a RAID 0 -- a simple disk mirroring.  Its for a production server
> > > that has to provide quick, dependable, and hands-off backup.  So, I
> > > figured two identical 40Gig drives mirrored should eliminate the
> > > possibility of a drive failure ever loosing data.
> >
> > Works like a charm, and is highly recommended! You can combine
> > multiple partitions from different drives into a raid array.
> > The partitions need to be of type "fd" (Linux raid autodetect).
> > You create the raid array with /etc/raidtab. Here is an example for
> > three raid-0 devices run off 2 IDE drives. The partitions in any one
> > RAID-0 device should be the same size (i.e, /dev/hda2 and /dev/hdc2 should
> > be the same size, for example, but hda2 and hda3 do not have to be the same).
> > Don't forget to include the raid stuff in your kernel. Once you set up
> > your your /etc/raidtab, run 'mkraid /dev/mdx', then 'mkreiserfs /dev/mdx'
> > and you are ready to go.
> >
> > -Borries
> >
> > raiddev /dev/md0
> >         raid-level              0
> >         nr-raid-disks           2
> >         persistent-superblock   1
> >         chunk-size              8
> >         device                  /dev/hda2
> >         raid-disk               0
> >         device                  /dev/hdc2
> >         raid-disk               1
> >
> > raiddev /dev/md1
> >         raid-level              0
> >         nr-raid-disks           2
> >         persistent-superblock   1
> >         chunk-size              8
> >         device                  /dev/hda3
> >         raid-disk               0
> >         device                  /dev/hdc3
> >         raid-disk               1
> >
> >
> > raiddev /dev/md2
> >         raid-level              0
> >         nr-raid-disks           2
> >         persistent-superblock   1
> >         chunk-size              8
> >         device                  /dev/hda4
> >         raid-disk               0
> >         device                  /dev/hdc4
> >         raid-disk               1
> >
> > >
> > > Thanks.
> > >
> > > Chuck
> > >
> > >
> > >
> > >
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