Maximum number of virtual disks and inconsistent naming of device files

[Trond Endrestøl]

On Wed, 16 Nov 2016 11:44+0100, Trond Endrestøl wrote:

> Hi,
> 
> I'm running XenServer 7.0.0. I tried to add the fourth, the fifth, and 
> the sixth drive to a FreeBSD VM running stable/11 r308642, with the 
> (almost unrelated) patch from r308126 applied.
> 
> The problem is that only the first three drives gets attached, the 
> last three drives are detected, but not acted upon:
> 
> xbd0: 12288MB <Virtual Block Device> at device/vbd/832 on xenbusb_front0
> xbd0: attaching as ada1
> xbd0: features: write_barrier
> xbd0: synchronize cache commands enabled.
> xbd1: 12288MB <Virtual Block Device> at device/vbd/768 on xenbusb_front0
> xbd1: attaching as ada0
> xbd1: features: write_barrier
> xbd1: synchronize cache commands enabled.
> xbd2: 12288MB <Virtual Block Device> at device/vbd/5632 on xenbusb_front0
> xbd2: attaching as ada2
> xbd2: features: write_barrier
> xbd2: synchronize cache commands enabled.
> xbd4: 2048MB <Virtual Block Device> at device/vbd/51776 on xenbusb_front0
> xbd4: features: write_barrier
> xbd4: synchronize cache commands enabled.
> xbd5: 2048MB <Virtual Block Device> at device/vbd/51792 on xenbusb_front0
> xbd5: features: write_barrier
> xbd5: synchronize cache commands enabled.
> xbd6: 2048MB <Virtual Block Device> at device/vbd/51808 on xenbusb_front0
> xbd6: features: write_barrier
> xbd6: synchronize cache commands enabled.
> 
> Can we get the three remaining drives attached as ada3, ada4, and 
> ada5?

I discovered the device files xbd{4,5,6} and created a zpool using 
these drives, so we can check this item off the list.

> Also, why is the naming of the device files inconsistent with the 
> drive order?
> 
> xbd0 => ada1
> xbd1 => ada0
> xbd2 => ada2 <= This one's consistent, but that's probably by accident.

Consistency would be nice.

> Are the drives 0, 1, 2, 4, 5, and 6, as shown in XenCenter, really 
> xbd0, xbd1, xbd2, xbd4, xbd5, xbd6?

I guess this is true.

> Wouldn't this mapping make more sense:
> 
> xbd0 => ada0
> xbd1 => ada1
> xbd2 => ada2
> xbd4 => ada3
> xbd5 => ada4
> xbd6 => ada5

This doesn't apply.

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