Kent Watsen wrote:
> Tommy/Mark,
>
> Thank you so much for your thoughts, you have helped me immensely
> crystalize my own...
>
> Mark - what did mean by "and of course, you need to think about
> migration, etc.. "? - that sound ominous...
Do you want to be able to move your guests between different
dom0s? If so, how do you plan to do this?
Kent Watsen wrote:
Hi Tommy,
I understand that sending a single raw device from the SAN to the DomU
would eliminate an extra layer of ZFS and hence provide a performance
boost but, if I understand you correctly, it would also eliminate the
redundancy my SAN delivers while also bounding my ability to grow
/export/home over time.
Specifically, my SAN has 24 SATA drives, which are in RAIDz2 - i.e.
4x(4+2) - a good balance between MTTDL and IOPS. If a take out 3 drives
to give to the DomU to use for its LUNs, with a zpool with matched
redundancy, I think I would be left with a less performant Dom0 zpool
(having taken out a stripe) and a difficult to grow DomU zpool (as I
couldn't simply allocate more from the SAN). That doesn't sound like it
justifies giving /export/home a small boost in performance...
Since you are exporting zvols from your san box, you
don't need one in dom0. i.e. if your using comstar and FC,
you can just pass on the disks directly to the domU.
I'm still somewhat new to storage, so please tell me if I'm missing
something
Have you thought about iscsi (the comstar iscsi stack is much
faster that the stock one that zfs uses)? This allows you
to be able to easily migrate your guests between dom0s..
We extended the phy:/ notation. The following options are
supported.
phy:iscsi:alias/<lun>/<iscsi-alias>
phy:iscsi:static/<server IP>/<lun>/<target id>
phy:iscsi:discover/<lun>/<alias or target id>
This way you can export zvols as iscsi LUNs directly to
the domU. The iscsi info doesn't have any dom0 specific
info, so when you migrate the guest, the hotplug scripts
will find the iscsi to /dev/dsk mapping for you.
virt-install -p -n nevada -l /export/snv129.iso --nographics --noautoconsole -r
1024 --mac 00:16:3e:72:9c:a8 --disk
path=/static/192.168.0.70/0/iqn.1986-03.com.sun:02:d5ab1c26-0a7a-c6b4-98f8-d6d267eb2561,driver=phy,subdriver=iscsi
virsh attach-disk nevada
/static/10.6.70.64/0/iqn.1986-03.com.sun:02:01accb27-35a3-e45f-882d-dc4e48c5685d
xvdb --driver phy --subdriver iscsi
MRJ
Thanks again,
Kent
On 1/26/10 11:26 PM, Tommy McNeely wrote:
ZFS is the best approach, but I agree with Mark, it would be best to
send the domU a *raw* device (target) from the SAN, rather than a zvol
if possible.
I have several other ideas about the "shared" home directories, but
totally understand where you are coming from with all the firewall
complex stuff, so I will let that be. When I used zones, I had one
/export/home per physical server, with xVM I have one per virtual
machine in my firewall complex, and I haven't sorted out what I want
to do there yet.
Good luck!
Tommy
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