Re: KVM, SCSI & OpenSolaris

[Anthony Liguori <anthony@codemonkey.ws>]

james wrote:
> The Use Case I am trying to achieve:
> 1. I have an AMD X4 with 4GB ram that is the central server. Given the 
> level of horse power it has the server does multiple roles, email, web 
> server, mythbuntu backend and file server.
> The base/host OS is Ubuntu 8.04 using standard packages so I am using 
> KVM-62. While I am prepared to uninstall this and move to a self 
> compiled KVM-70 I want to determine if that move is worth it based on 
> my target outcome, or if I need to move to an alternative VM solution.
>
> 2. The desire is to get the file server role moved from running LVM to 
> ZFS raidz to allow "easy" upgrades of disk size on a disk by disk 
> basis (not available as an option under normal raid 5). e.g. pull out 
> a single 320GB disk and put in a 500GB or 750GB disk into the raidz 
> and it all "just works" still with the extra storage being available.
>
> 3. Looking to achieve this move by using a VM running either 
> OpenSolaris or Nexenta. The idea being to have the VM as a NAS setup 
> to be using the disks directly as block devices. So the setup is to 
> have a a boot img (can be IDE) and 4 other direct access block devices 
> (need to be SCSI as there are not enough IDE devices available). Not 
> these are all 64 bit installs based on the advice that ZFS needs a 64 
> bit OS to behave well.
>
> 4. Options tried:
> a] I have tried using FreeBSD 7 using ZFS under this VM model. However 
> when put it under load I get scsi errors an the VM segment 
> faults/core-dumps. This is
> b] I have been trying to get OpenSolaris and Nexenta (basically the 
> same at the core) working but neither recognise the KVM scsi 
> controler. It seems to coming through as id PCI1000,12 which is a 
> LSI53C895A PCI to Ultra2 SCSI Controller which is supposed to use the 
> symhisl driver. Now from good old Google I have found that there are 
> supposed to be problems with this driver and it will not be ported to 
> 64 bit. Indeed looking at the OpenSolaris /etc/driver_aliases this 
> driver to PCI mapping has been dropped.
>
> 5. So the questions are:
> a]  How stable/robust is the scsi implementation under KVM? i.e. are 
> there known weaknesses here that moving to higher KVM versions will 
> address such that using FreeBSD 7 will be a viable option.

It hasn't been tested much (if at all) with the FreeBSD 7 drivers.  In 
fact, I don't think there's been much testing at all of FreeBSD as a 
guest in KVM.

> b] It would appear that KVM has a general exposure in the SCSI space 
> for OpenSolaris and its variants. Due to dropped driver support the 
> current SCSI implementation on KVM will no longer work with 
> OpenSolaris (at least in its 64bit variant). Or is this resolved in 
> later KVM versions (after KVM-62)?

I don't quite following what you are saying.  Are you saying that 
OpenSolaris no longer supports the SCSI card we emulate?  That seems 
unfortunate on their part.  I would also be surprised by that since the 
same SCSI implementation is used by Xen and Sun is heavily invested in 
OpenSolaris for Xen at this point.

Regards,

Anthony Liguori

> All help and suggestions gratefully received.
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