I am under the impression from documentation and misc list archives,
that openbsd doesn't support logical volumes only CCD.
Also I am planning on booting from the array, to gain the benefits of
fail-over from the array.
On Feb 17, 2006, at 1:52 PM, Otto Moerbeek wrote:
On Fri, 17 Feb 2006, Vincent Meanie wrote:
I have reviewed many faq's and searched the mailing list archives
but found
nothing.
I am currently in the process of a major upgrade from an existing
system that
has been in collocation for three years, openbsd 3.5 with Pentium
3 hardware
and 400gb total storage. The system hardware replacing it will
have a hardware
sata raid controller, and the original plan was to present the
Array as one
2.1tb drive to Openbsd 3.8. The initial headache was obtaining all
the
hardware.
Reviewing documentation revealed this gem:
14.7 - What are the issues regarding large drives with OpenBSD?
OpenBSD supports an individual file system of up to 231-1, or
2,147,483,647
sectors, and as each sector is 512 bytes, that's a tiny > amount
less than
1T.
There is also a 1T limit on the size of the physical disk,
although under
*some* circumstances, that may not cause you problems up to 2T,
although
this
is not guaranteed.
Is this hard limit because of issues with the filesystem? Would it be
possible, limitations with the controller aside, to present the
array as three
700mb slices and combine them with CCD? Or would I be faced with
the same
limitation because of the large disk size.
Yes. The 1TB disk limit is a limitation caused by the fact that a 32
bit signed number is used to address disk sectors. 2^31 * 512 = 1TB.
The array is running raid 5 which is the reason for the large disk
size.
Just divide the array up into logical volumes, but do not combine them
using ccd(4), but by mounting.
Lets's say you create 3 logical volumes. You create filesystems on
them, and mount them. Since your setup probably has some top level
dirs anyway, you can use those as mount points. It requires some
planning, but should not be that hard.
Not that creating very large filesystems also has some drawbacks:
mostly very long fsck times and high memory consumption. Also, after a
crash, fsck'ing the logical volumes can take VERY long, since by
default the system thinks the logical volmes are separate disks and
fsck them in parallel, so all disk i/o will go to the same disks. Use
the -l parameter to fsck to avoid that.
-Otto
I am really stuck on this problem as Openbsd is my primary OS
choice, but this
is a deal breaker and I would like to explore all options before
having to
move to another OS.
Thank you for your time.
