[kwlug-disc] RAID-0 for the first time

Khalid Baheyeldin kb at 2bits.com
Wed Feb 24 22:31:48 EST 2010


On Wed, Feb 24, 2010 at 10:18 PM, Richard Weait <richard at weait.com> wrote:

> I'm playing with RAID-0 for the first time.  There are three disk
> drives; one (500GB) for Operating system and everyday stuff, and two
> additional identical drives for RAID-y stuff.
>
> The OS is installed and working fine, thanks for asking.  ;-)
>
> For the RAID-0, it might actually be installed and working properly,
> but df -hT reports too much capacity on the RAID drive.  In fact it
> reports roughly the sum of the capacity of the two RAID drives.  I was
> expecting roughly the capacity of one of the identical RAID drives to
> be reported as the capacity of the RAID-0 array.
>
> I set it up like this
>
> Partition two drives
> - each of the two (sde, sdf) were partitioned (fdisk) with a single
> partition, primary, 1, all sectors.
> - and a type of Linux raid auto (df)
>
> Create RAID-0 from two partitions
> sudo mdadm --create /dev/md0 --level=0 --raid-devices=2 /dev/sde1 /dev/sdf1
>
> Add filesystem to RAID-0
> sudo mke2fs -j /dev/md0
>
> Make a mount point for it
> sudo mkdir /raid
>
> Mount it
> sudo mount /dev/md0 /raid
>
> But df thinks the RAID-0 drive is too big.
> df -hT
> Filesystem    Type    Size  Used Avail Use% Mounted on
> /dev/sdg1     ext4    440G  6.0G  412G   2% /
> /dev/md0      ext3    1.8T  196M  1.7T   1% /raid
>
> Wazzup with that?  Does df just not get RAID, or did I hose the RAID setup?
>

Hmm .. Interesting ...

It seems to be doubling the capacity [ (500+500) x 2 less filesystem
overhead, and GiB vs. GB difference].

But let us step back a bit ...

Do you REALLY want RAID-0?

You know that if one drive fails, then ALL your other drives are close to
useless?

Use it for transient stuff (e.g. print spool, Usenet spool, ...etc.), but
not for anything else that you really need ...


-- 
Khalid M. Baheyeldin
2bits.com, Inc.
http://2bits.com
Drupal optimization, development, customization and consulting.
Simplicity is prerequisite for reliability. --  Edsger W.Dijkstra
Simplicity is the ultimate sophistication. --   Leonardo da Vinci
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