Phillip Susi psusi at
Sun Jan 1 01:22:42 UTC 2006

Anders Karlsson wrote:
> You are correct though that LVM2 and device-mapper is the same thing.

They are not the same thing really.  LVM uses device mapper, but LVM 
encompases a host of user mode utilities and on disk meta data 
structures that the device mapper is not at all aware of.  The point of 
device mapper is to allow things like raid volume detection, disk 
partition detection, and other things to be moved out of kernel space to 
user mode management utilities where they belong, and keep the kernel 

> The hardware fakeraids are mostly a waste of time and effort. dmraid
> may be able to manipulate them, but IMO (and I have such a card) you'd
> be better off disabling the fakeraid and using MD.

Hardware fakeraid has several advantages over md including:

1) Can dual boot with windows
2) Can boot directly from the raid, rather than have a seperate boot 
3) Can boot from volume types other than raid1 ( i.e. raid0 )
4) In the event that the primary drive in a mirror fails, the system 
still boots using the second drive rather than hang trying to read the 

I very much enjoy booting up from a stripe of two 10,000 rpm 36 gig sata 
WD raptors which give a combined sustained read throughput of very 
nearly 100 MB/s, and it's nice to have a copy of windows on there too 
for the occasional game fest.

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