[mythtv-users] Linux software raid question

Carl L. Gilbert clg-social at rigidsoftware.com
Wed Jun 11 13:15:30 UTC 2008

On Tue, 2008-06-10 at 10:49 -0400, John Drescher wrote:

> >Last time I "booted" on software RAID it was not really on the RAID.  There were simply 2 exactly the same partitions on both drives that >were boot.  But if you removed a drive, then you had to go into BIOS to tell it to boot from the other drive because it was not truly RAID at >that point.  Just duplicate.  Plus if you change the boot you have to remember to copy it to both drives.
> >Unless the RAID driver is now somehow included in the boot manager!?
> That is the point about the very small raid 1 partition where all
> members have the exact same contents. Linux software raid will mirror
> this partition to all drives in the array. The BIOS will see these as
> individual bootabe partitions. Its propose of this is to hold just the
> kernel. This allows you to not have to have an extra drive just to
> boot. I do not see this as a disadvantage to software. If I was forced
> to have the entire raid array at only one raid level I would still
> have a small boot partition.

I know, but what happens when a drive fails.  I switched to hardware
RAID not because of runtime performance, but because of ease of recovery
in failure.  It does not matter if the partitions are mirrored.  Either
you have the bootloader in the MBR, or on the boot sector of an
individual partition. The BIOS will only point to a single bootloader
and if the drive with that fails, you must go into BIOS and change it.

> > I call this an advantage over hardware. I mean I get  my 256 MB boot
> > and my 50GB / back under full raid level in a less than 30 minutes
> > instead of waiting for hours..
> >
> >
> > I don't wait for hours if the drive was properly shut down.  When I did
> > software, that took a long time too if you did not properly shut things
> > down.
> >
> Here I am talking about when replacing a bad drive. On software raid,
> I do not see any of these shutdown problems anymore. How many times
> does a linux system that is connected to a UPS not properly shut down?
> For me this is a less frequently than replacing a bad drive.

So your saying SW RAID resyncs faster than HW RAID?

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