[linux-lvm] Re: raid 1 on a single disk

Piete Brooks Piete.Brooks at cl.cam.ac.uk
Sat Nov 13 13:38:14 UTC 2004

> (please do not top post - fixing. Please take note!)
(what's "top post"ing?)

>> ok so, i also do know, its performance is going to suck ! 
> No, it'll be fine - merely a couple or more times slower at writing
> large streams.

Actually, over 4 times :-(

He has a 4 way mirror on hdd.
As well as having to send all date over the (same!) IDE bus 4 times,
the disk head keeps having to move between the 4 partitions :-(

> What's silly is that there's no point in doing it

Not true -- there is little point.

It will protect against un-re-vectored block faults.

> you get no protection against the disk disappearing

Indeed -- which is the real use for RAID1 ...

> It's like making 3 sets of spare housekeys, and then putting them all
> in the same keyholder as the original set, and walking around like that.

Which has *some* use if the keys are made of very soft metal and "wear out".

[ His actual problem was that he didn't realise that mkraid is brain dead, and 
needs a chunk size in /etc/raidtab, even when it's not used!  I showed him how 
to use mdadm, and it worked ]

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