[plug] Good RAID Howto

[Adam Davin]

Hello Kai,

On Wed, 14 Sep 2005 09:12:28 +0800
Kai Jones <kai.jones at broome.wa.gov.au> wrote:

> Running "dmesg | grep sd" gives the following:
> 
> Attached scsi disk sda at scsi0, channel 1, id 0, lun 0
> SCSI device sda: 71127040 512-byte hdwr sectors (36417 MB)
>   sda: sda1 sda2 < sda5 sda6 sda7 >
> 
> I'm guessing this means sda, sda1 and sda2 are the active RAID1 and 
> sda5, 6 and 7 are spares because it doesn't yet know the 3 x 73 gig 
> disks are plugged in and waiting ?

<snip>

<disclaimer> 
I haven't really been following this thread but, 
</disclaimer>

As my understanding of the partitions in linux goes, sda is a single
drive (The first scsi drive <s>csi <d>isk <a>, followed by sdb sdc
etc) and sda1, sda2 are primary partitions 1 and 2 on the drive sda.
sd5, sd6 ans sd7 are logical partitions 5, 6 and 7 inside the extended
partition (usually the next available primary partition number?) 
denoted by "< ... >".
 If sda1 and sda2 are raided (mirrored) together, you are
weakening the strength of having a raid system as the partitions are
residing on the same drive. If you end up with bad sectors on one of the
partitions you might be able to save your data, however, if your drive
dies completely, you will loose everything. 

If you already knew all this then my apologies. I don't like to see
people having false warm fuzzy feelings when their data might not be as
save as they thought it was. 

Hope this helps, 

Regards

-- 

Adam Davin
Byteme IT Services
Mob: 0422 893 898
Email: byteme-its at westnet.com.au