On Wed, Jul 21, 1999 at 05:21:54PM -0700, D. Lance Robinson wrote:
> James,
>
> There are currently 128 possible SCSI disk device allocated in the
> device map--see linux/Documentation/devices.txt . Now, each of these
> supports partitions 1..15 (lower 4 bits) with 0 being the raw device,
> and the other bits for the base device are mapped into various places.
> There is a slight chance of modifying things so that you have less
> partition bits and give those unused bits to the base scsi devices. I
> don't know how well disciplined the scsi code is in using the conversion
> macros from device and partition to device number.
I had a conversation (email) with Alan Cox on this, back when the
limit was 5 or 6 disks (or so). I hacked a #define or two to increase
the limit, but in the meantime, someone else did a real fix that
raised this limit to what it is today. You could try asking Alan
(or whoever has his name in scsi.[ch] :) about the possibilities
for increasing the number of disks even further. It _ought_ to be
pretty simple to allocate a few more major numbers, since AFAIK the
SCSI disks alreay span a few major numbers (non-consecutive).
> You have another problem with the md driver (raid). It's superblock is
> coded to allow raid sets of up to 11 devices (12 if you count the
> spare.) This is a #define set to 12. You should be able increase this
> value to 16 and recompile the kernel and tools.
You can't, AFAIK. It has something to do with the number of bits in
the RAID superblock. Ingo has been working on increasing this limit,
and he has something up running, but it seems the code still need
some adjustments.
I'm sure that Ingo would be happy to have someone with such hardware
test his patch ;)
>
> I have heard of a large file patch for ext2 filesystem that you may be
> able to use. FYI: the ext2 filesystem is limited to 1-Terabyte maximum
> per volume.
I thought it was 2T. Oh, never mind. It's still below the 8T we're talking
about here.
Really, are you sure you need a file system at all ? If you will be
running some special application that generates/gathers huge amounts
of data, a tiny C program can often do the trick just as well, on a
raw disk. You can still do fast seeks, and if the data is to be read/
written sequentially anyway, it may well be a viable solution. No need
to bother about fsck, vfs, 31-bits, etc. etc.
Cheers,
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