Re: Newbie questions: Max Active disks, RAID migration, Compiling mdadm 2.3

[Mike Hardy <mhardy@h3c.com>]

If you remove the '-Werror' it'll compile and work, but you still can't
convert a raid 0 to a raid 5. You're raid level understanding is off as
well, raid 5 is a parity block rotating around all drives, you were
thinking of raid 4 which has a single parity disk. Migrating raid 0 to
raid 4 (and vice versa) should be possible technically, but I don't
think it's implemented anywhere

You should be able to have more than 4 active drives though. I am at
this moment building an array with 6 components, I'm running a few with
more than that, and these are by no means the largest arrays that people
are running - just examples of it working.

-Mike

Martin Ritchie wrote:
> Sorry if these are total newbie questions.
> 
> Why can't I have more than 4 active drives in my md RAID?
> 
> Why can't I easily migrate a RAID 0 to RAID 5. As I see it RAID 0 is 
> just RAID 5 with a failed parity check drive?
> 
> Perhaps this is a limitation of the old v1.11 that FC4 updates to.
> 
> I tried to compile 2.3 but I get this error:
> 
> $make
> gcc -Wall -Werror -Wstrict-prototypes -DCONFFILE=\"/etc/mdadm.conf\" -
> ggdb -DSendmail=\""/usr/sbin/sendmail -t"\"   -c -o super0.o super0.c
> In file included from super0.c:31:
> /usr/include/asm/byteorder.h:6:2: error: #warning using private  kernel
> header; include <endian.h> instead!
> make: *** [super0.o] Error 1
> 
> I'm not too familiar with compiling this sort of thing. (I usually  live
> further away from the hardware and endian issues). I'm guessing  there
> is some sort of option i have to specify to say that this  should use
> the private kernel headers. Including endian.h instead  didn't help:
> 
> $make
> gcc -Wall -Werror -Wstrict-prototypes -DCONFFILE=\"/etc/mdadm.conf\" -
> ggdb -DSendmail=\""/usr/sbin/sendmail -t"\"   -c -o super0.o super0.c
> cc1: warnings being treated as errors
> super0.c: In function ‘add_internal_bitmap0’:
> super0.c:737: warning: implicit declaration of function ‘__cpu_to_le32’
> super0.c:742: warning: implicit declaration of function ‘__cpu_to_le64’
> make: *** [super0.o] Error 1
> 
> Oh just because I know it is going to be an issue I'm building on a 
> Athlon 64... my first 64bit linux box so I'm sure there are going to  be
> gotchas that I've not thought about.
> 
> Is there somewhere I over looked for finding this information.
> 
> TIA

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