psusi at cfl.rr.com
Sun Jan 1 16:56:23 UTC 2006
Anders Karlsson wrote:
> MD does that as well, I have such a setup. I would agree that if you
> want to gamble your data on a RAID0 setup, *then* the fakeraid may be
> your only option *if* you insist on striping across the whole disks
> and not keep your root/boot partition separate from the RAID0.
>>3) Can boot from volume types other than raid1 ( i.e. raid0 )
> See above.
No, md definately does not support directly booting from the raid. The
bios and grub have no understanding of the md raid, they can only boot
from a stand alone disk/partition. If md is mirroring, then both disks
are the same, so the bios+grub can boot from one as if it were a stand
alone disk. With raids other than raid1, this is not possible so you
have to set up a seperate /boot that is either stand alone or mirrored.
>>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
> That will hold true for MD as well. The whole point of mirroring is
> that both (all) copies are equal, and contain the same data.
No, it won't because the bios only tries to boot the first disk as if it
were not part of a mirror. If that fails, the system doesn't boot. The
bios and grub can not fail over to the second disk on error
automatically like the kernel md driver can, so in the event that
something goes wrong on the first drive, you will have to unplug the
first drive and use only the second drive in the mirror to boot.
> Why oh why these fakeraid cards are incapable of 'hiding' the raid
> members they have attached, and present logical devices through int
> 13h instead like sane raid controllers is beyond me. I do regret not
> calling bull on the adapter I bought, and either spending less on a
> normal pic ide card, or spending more getting a proper raid card.
> Each one to their own I guess.
They ARE capable of presenting a single disk via int 13h, that is their
entire point. That is what makes them hardware (fake)raid and is what
allows them to be bootable. In windows you load a driver that also
presents a single disk to the OS, but in linux the driver only shows the
individual disks, and leaves the raiding up to the device mapper.
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