filesystem size in RAID 5

jason andrade jason at dstc.edu.au
Wed Nov 6 18:48:01 CST 2002


On Wed, 6 Nov 2002, Alexander Lazarevich wrote:

> we just got a PowerEdge 4600, dual 2.8 GHz, 2 X 73GB in RAID 1 (for the
> system), and 8 X 73GB in RAID 5 (for fileserving). running linux 7.3 which
> was preinstalled.

very nice.

> 1) is there any good reason to keep the linux preinstall? id really like
> to just reinstall everything myself. i noticed that dell has a utility
> partition. what is that? the RAID and BIOS utilities are not effected if i
> blow away that partition, right?

it depends on who is doing your support.  if you are using a support
contract (through dell/redhat) it might be advisable to stay with a
vanilla system which is in a configuration which is tested by your
vendor.

if you have local unix sysadmin resources then there is no reason not to
reinstall in a configuration that might better suit your requirements.

> 2) concerning the RAID 5 array, the max ext3 filesystem size i can make on
> it is 469GB, when the actual "disk" size should be 512GB (73GB X 4). is
> this normal, or am i hitting some limit in linux? im assuming its normal,
> maybe the journal is taking up a lot of space, but i just want to make
> sure.

i am assuming the above is a typo and you mean 73*8.  you will lose some disk
space depending on your ext3 creation options.  you also do lose a bit to some
of the overhead during raid creation (is this hardware or software raid?) and
rounding stuff down.

if you create with less inodes, you should have more space.  you should also
consider using tunefs to reduce the "reserved space" from 5% to 1%, e.g

tunefs -m 1 /dev/mdX or /dev/sdX

(preferably on an unmounted filesystem)



regards,

-jason




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