The case against LVM

[Mikkel L. Ellertson]

Rick Stevens wrote:
> On Thu, 2007-08-09 at 18:58 -0500, Mikkel L. Ellertson wrote:
>> From what I understand, there are a max of 16 device entries created
>> for a SCSI hard drive. (sdx and sdx1 through sdx15) So while you can
>> have more partitions then that, Linux will not let you access them
>> when using the SCSI code to access the drive. I believe it is a
>> driver problem more then a udev problem.
> 
> Well, the "x" in your example can take the RE form "[a-z]+".  For
> example, we have some storage arrays with, oh, 130 LUNs on them.  They
> appear as /dev/sda[1-15] through /dev/sdiv[1-15]
> 
> As far as the partition numbers, that's based on the minor number of the
> block device.  The formula is "(16 * drive number) + partition number".
> The "16" is what limits it to 16 partitions (with partition 0 being the
> same as the whole drive, e.g. "/dev/sda0" is the same as "/dev/sda").
> 
> "man sd" will show you the magic.
> 
You and I are saying the same thing, just in different ways. I used
x where you use [a-z]+. But I have never seen /dev/sda0 created. It
is always /dev/sda. You could also argue that the entire disk is not
a partition, even though you can access the entire disk as if it
were a partition. (You can create a file system on /dev/sda, but you
can not do that and have a partition table at the same time.) There
have been times in the past where I have used the entire drive
instead of creating a partition table. But most BIOS do not like it.
(Tar doesn't care - the drive can be one big archive.)

When you get into SCSI LUNs, you will probably lose a lot of people.
I have always found it easier to think of each LUN as its own
device. But then again, I worked more with CD drive arrays connected
to a LUN controller. 8 drives  using one SCSI device number. Now
days, it usually works better to copy the CD images to a hard drive,
and loopback mount them. By using automount to manage them, you can
even keep the number of loopback mounts down to a reasonable number.

Mikkel
-- 

  Do not meddle in the affairs of dragons,
for thou art crunchy and taste good with Ketchup!

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