David Vasek wrote:
Hi all,
is there any guide about compatibility of (OpenBSD) FFS filesystem and
disklabel among different hardware platforms? As I understand it, FFS
filesystems on architectures with different byte endianess are not
mutually compatible. What about different word length with same
byte-endianess? Is FFS2 any different in this respect? The FAQ suggests
that that i386 and amd64 are not mutually compatible.
From http://www.openbsd.org/faq/faq12.html#amd64better :
12.3.3 - Is it always better to run OpenBSD/amd64 on processors that
support it?
Not always.
There are a number of reasons one may desire to use OpenBSD/i386 over
OpenBSD/amd64, even on hardware that supports amd64 code:
[...]
* Need for ability to move disks to another machine that isn't amd64
capable
[...]
Do I understand it right that disks (FFS, disklabel?) from OpenBSD/i386
cannot be accessed on OpenBSD/amd64 or vice versa?
ACCESSED, yes, you can access data on your amd64 disks on an i386 system.
That sentence was intended to refer to repair. If your amd64 system
craps out and you need to pull the disks out and put it in another
machine and have it Just Work (or work with minimal effort), you need to
have another amd64-compatible processor. That wasn't referring to a
file system issue, but rather a rapid repair issue.
I want to share
external backup disks among different architectures and do not want to
screw my data. What is the solution then?
There are lots of issues when moving disks between platforms. Even if
FFS on a sparc64 and an i386 and a MacPPC weren't issues, they each
handle the disk differently (i.e., i386/amd64 use the fdisk & disklabel
layout, sparc/sparc64 use just disklabel, macppc uses pdisk & disklabel
OR fdisk & disklabel). Enough issues that I think you are best off just
planning on putting a disk on a box and leaving it there. (You may
actually get away with a bit more for non-boot disks as long as you
respect endian issues...but you will have to play with it).
Best way I know of to back up a lot of odd machines is to one store is
running your favorite backup application so it dumps its data over ssh
link to the one machine (which you have a spare of for repair purposes)
which has the backup media attached to it.
however, if "Different architectures" means amd64 and i386, no issues at
all.
Nick.
