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List:       xen-users
Subject:    Re: [Xen-users] Extending a disk attached by iscsi
From:       Adam Goryachev <mailinglists () websitemanagers ! com ! au>
Date:       2016-11-29 22:09:03
Message-ID: f7b85eee-c2f3-b58e-a41b-cd86b21ba684 () websitemanagers ! com ! au
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On 29/11/16 23:32, Austin S. Hemmelgarn wrote:
> On 2016-11-29 07:28, Austin S. Hemmelgarn wrote:
>> On 2016-11-28 17:26, Lang, Adam wrote:
>>> Hello,
>>>
>>>
>>>
>>> I inherited an old Xen environment with one VM remaining that we 
>>> need to
>>> use for the foreseeable future.
>>>
>>> xen_caps               : xen-3.0-x86_64 xen-3.0-x86_32p
>>>
>>>
>>>
>>> A disk for the VM is mapped via iscsi on a Dell Powervault for 2
>>> terrabytes.  I increased the virtual capacity of the mapping on the
>>> powervault to over 3 terrabytes, but the actual VM still only 
>>> recognizes
>>> 2 TB.
>>>
>>>
>>>
>>> I can't seem to find the appropriate way to have Xen recognize the
>>> larger capacity and the only Xen/iSCSI docs I see online are about 
>>> newer
>>> Citrix oriented platforms.
>>>
>>>
>>>
>>> If anyone can share ideas or where I can look, it would be appreciated.
>> This really depends on how the disk is actually attached.  If you're
>> using regular Xen then Xen itself is not handling the iSCSI stuff
>> (XenServer does though, which is why you see the Citrix stuff when
>> searching).  Assuming that the guest isn't mapping the device itself
>> (which may be more efficient in some cases), then:
>> * For a HVM domain, it's the device-model (QEMU) doing the handling, so
>> you'd need to look at that.
>> * For a PV domain, it's handled by the Domain-0 OS (so for this, check
>> the docs for whatever you're using for your Domain-0).
>>
>> In either case, your guest OS may be limiting things too (2TiB - 1 byte
>> is a common storage stack limitation because that happens to be roughly
>> 2^48 (and many older systems only support 48-bit LBA)).  If the VM is
>> older than a few years, this is actually what I would suspect first, not
>> some other configuration issue.
> Realized almost immediately after I sent this that I meant 512 * 
> (2^32), not 2^48, and a 32-bit max sector count, not 48-bit LBA....
>

It might be a good idea to check your dom0 xen config file.
For me, I need to do the following steps when growing a disk for a VM:
1) Increase the LV size on the iscsi server (on both of them)
2) tell DRBD to increase the size of the disk
3) restart iscsi on the server to "see" the increased size (I actually 
do this by failing over from primary to secondary)
4) reboot the dom0 (migrate all VM's to another dom0 first)
5) reboot the domU that needs the increased disk (depending on if it is 
a PV or HVM)

You should check the size of the LV, check the size of the disk that 
your dom0 can see, and then check the size of the disk your domU can 
see. If the dom0 sees the bigger size, but domU doesn't, then stop/start 
the domU. If the dom0 doesn't see the bigger size, then reboot it. If 
that doesn't help, then reboot the iSCSI server.

PS, reboot is really just the easy option, there are probably better 
ways, but it's a global thing, restart all services, refresh kernel view 
of devices, etc...

Failing all of the above, then it could indeed be some 2TB limit, I 
don't have any that are that large, my largest is only 880GB.

Regards,
Adam

-- 
Adam Goryachev Website Managers www.websitemanagers.com.au

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