[Novalug] best hard disk setup for home file server?

[Bryan J Smith]

DeviceMapper can stripe the mirrors along with original data
in nearby cylinders, and not at the other side of the disk.  Yes,
DeviceMapper is not cake to configure advanced operations, but
it can do many things people have never tried.

------Original Message------
From: James Ewing Cottrell 3rd
To: Bryan J. Smith
Cc: Aaron Porter
Cc: Brandon Saxe
Cc: Novalug
Sent: Oct 16, 2009 13:21
Subject: Re: [Novalug] best hard disk setup for home file server?

i think he wants specifics. his, and my assumptions are that it makes no 
sense to stripe or mirror to a different partition on the same disk 
within the same file system. in other words, the following make sense:

m1=mirror(sda1, sdb1); fs1=ext3(m1);
s1=stripe(sda1, sdb1); fs1=ext3(s1);

but these make little sense

m1=mirror(sda1, sda2); fs1=ext3(m1);
s1=stripe(sda1, sda2); fs1=ext3(s1);

in the first case, you are protecting only against the failure of part 
of the disk surface, not the whole unit, and in both cases, you are 
turning your cylinder arm into an oscillator.

ultimately, you need 4 partitions, and if you want to protect against 
disk failure, the mirrors have to be on different disk. and the only 
reason to stripe within a disk is if you want concatenation to increase 
the maximum partition size limit. otherwise, striping loses.

jim

Bryan J. Smith wrote:
> You could have 2 mirrors (3 copies) as well, striped over the disks.
> That would survive two disk failures.
> 
> Or you could have 1 mirror (2 copies) whereby one copy is over
> 2 disk while the other copy is over 2 disks.  You could only survive
> one disk failure though.
> 
> Again, you only need 2 disks for RAID-0+1.  You stripe and then
> mirror to the other disk that does not contain the stripe.  It can survive
> one disk failure.


--  
Bryan J Smith - mailto:b.j.smith at ieee.org  
http://www.linkedin.com/in/bjsmith
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