Re: Resizing a zpool as a VMware ESXi guest ...

On 11/27/2015 7:44 PM, Matthew Grooms wrote:
> I spent the day looking over the FreeBSD cam and scsi_da source code. 
> After sprinkling a bunch of printf's around to see what code paths 
> were being called, It's obvious that Edward was correct in assuming 
> that ESXi doesn't return any 'Unit Attention' sense information in 
> response to a 'Read Capacity' request. This kinda makes sense as ESXi 
> emulates SCSI-2 disk devices and, as far as I can tell, the 0x2A/0x09 
> ASC/ASCQ sense code that denotes 'Capacity Data Has Changed' wasn't 
> defined until the SCSCI-3 spec. It's frustrating that the only way to 
> get the scsci_da code to call reprobe() is by receiving a command from 
> the device. Would something like this work? ...
>
> 1) Register a callback using xpt_register_async( daasync, 
> AC_REPROBE_DEVICE, path ) that calls reprobe()
> 2) Implement a new IOCTL in cam_xpt that camcontrol can call with the 
> bus:target:lun as the argument
> 3) have cam_xpt capture the IOCTL request and call xpt_async( 
> AC_REPROBE_DEVICE, path ) as a result
>
> This way users would have the option of manually asking cam to 
> communicate the new size to geom. The only option now is one or more 
> reboots to gain access to the increased disk capacity. If this sounds 
> like a reasonable approach, I'll take a stab at implementing it.
>

Here is a proof of concept patch. I'm a complete noob when it comes to 
cam, scsi or freebsd kernel development for that matter, so I'm sure it 
could have been done a better way. In any case, I added a new command to 
camcontrol that allows you to specify a bus, target and lun as an 
argument. For example ...

# camcontrol readcap da1 -h
Device Size: 32 G, Block Length: 512 bytes

# gpart show da1
=>      40  58720176  da1  GPT  (28G)
         40  58720176    1  freebsd-ufs  (28G)

Note, I resized the VMDK disk in ESXi. The camcontrol output shows the 
size as 32G but geom thinks its 28G.

# camcontrol devlist
<NECVMWar VMware IDE CDR10 1.00>   at scbus1 target 0 lun 0 (cd0,pass0)
<VMware Virtual disk 1.0>          at scbus2 target 0 lun 0 (pass1,da0)
<VMware Virtual disk 1.0>          at scbus2 target 1 lun 0 (pass2,da1)
<FREEBSD CTLDISK 0001>             at scbus3 target 0 lun 0 (da2,pass3)

# camcontrol reprobe 2:1:0

This generates an event that is captured by the scsci da device to 
forces a reprobe. The kernel output looks almost identical to when the 
'Unit Attention' sense data is received ...

Nov 28 17:46:13 iscsi-i kernel: (da1:mpt0:0:1:0): Re-probe requested
Nov 28 17:46:13 iscsi-i kernel: GEOM_PART: da1 was automatically resized.
Nov 28 17:46:13 iscsi-i kernel: Use `gpart commit da1` to save changes 
or `gpart undo da1` to revert them.

Now that geom knows about the increased disk capacity, I can increase 
the partition size and grow the fs ...

[root_at_iscsi-i /home/mgrooms]# gpart show da1
=>      40  67108784  da1  GPT  (32G)
         40  58720176    1  freebsd-ufs  (28G)
   58720216   8388608       - free -  (4.0G)

# gpart resize -i 1 da1
da1p1 resized

# growfs da1p1
Device is mounted read-write; resizing will result in temporary write 
suspension for /var/data1.
It's strongly recommended to make a backup before growing the file system.
OK to grow filesystem on /dev/da1p1, mounted on /var/data1, from 28GB to 
32GB? [Yes/No] Yes
super-block backups (for fsck_ffs -b #) at:
  58983232, 60265472, 61547712, 62829952, 64112192, 65394432, 66676672

# df -h
Filesystem    Size    Used   Avail Capacity  Mounted on
/dev/da0p3     18G    5.3G     12G    31%    /
devfs         1.0K    1.0K      0B   100%    /dev
/dev/da1p1     31G     32M     28G     0%    /var/data1
/dev/da2p1     15G     32M     14G     0%    /var/data2

Sure would be nice to have something like this in the tree. It's really 
a drag to have to reboot production VMs to increase disk capacity when 
it could be easily avoided. I'm not sure what the correct IOCTL should 
look like. Maybe CAMIOCOMMAND is a better way to go? If someone with 
some experience with the cam/scsi subsystems was willing to give me some 
direction I'd be willing to try and rewrite the patch in a way that 
would be commit worthy. I just need some direction.

Thanks,

-Matthew