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<div class="moz-cite-prefix">On 08/21/2015 05:30 PM, Tom Buskey
wrote:<br>
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cite="mid:CAEHDbACb0xCP8htsPHhA9xaBvXzGDsOv2bsBe76roQE8Rvi25Q@mail.gmail.com"
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<div class="gmail_quote">On Fri, Aug 21, 2015 at 3:33 PM,
Bruce Dawson <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:jbd@codemeta.com" target="_blank">jbd@codemeta.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
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<div bgcolor="#FFFFFF" text="#000000"> For this rainy
weekend, please consider the following:<br>
<br>
I'm constructing a new server and want 2 KVM guest
systems on it. There are 3 4TB drives on it. At the
moment, assume one 4TB drive will be reserved for the
KVM host. The server has 16GB of RAM.<br>
<br>
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<div>I've been running ZFSonLinux for awhile. Now on CentOS
7, but previously on Ubuntu. And OpenSolaris before that.</div>
<div><br>
</div>
<div>I typically do a minimal OS with 2 smaller disks with
RAID1 mdadm. I like to make my OS disks independant of
any driver or OS addons. I don't know how good Linux
booting on ZFS is either. Actually, I don't even know if
it's possible. I think it is with BSD.</div>
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<br>
Ubuntu 14.04 will supposedly boot from a ZFS root.<br>
<br>
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cite="mid:CAEHDbACb0xCP8htsPHhA9xaBvXzGDsOv2bsBe76roQE8Rvi25Q@mail.gmail.com"
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<div>I do ZFS on my data disks (no dedup!). ZFS could do a
RAIDZ of the unused space in a partition of the OS drive +
the same partitions of the other drives, but it really
prefers whole disks and works better. Plus, all drives
should be the same size.</div>
<div> <br>
</div>
<blockquote class="gmail_quote" style="margin:0 0 0
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<div bgcolor="#FFFFFF" text="#000000"> What are the
advantages/disadvantages of:<br>
<ol>
<li>Putting all disks in a ZFS pool on the host and
dividing the pool between each guest. Or:</li>
</ol>
</div>
</blockquote>
<div>So you're going to use one drive for the OS w/o ZFS?
Then 2 drives for ZFS & data?</div>
<div>Then using zfs commands to allocate space to the
guests? I do this all the time.</div>
<div> </div>
<blockquote class="gmail_quote" style="margin:0 0 0
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<ol>
<li>Giving each guest its own disk. (At least one of
the guests will be running ZFS).</li>
</ol>
</div>
</blockquote>
<div>I wouldn't ever run ZFS on a single disk if I cared
about the data. It's like running RAID0; get an error,
you lose your all your data. Actually, you might recover
data from a RAID0 non-ZFS.<br>
</div>
</div>
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<br>
Oh - but I thought ZFS will mirror "filesystems" within the pool
(probably with much poorer performance)? At any rate, I'm thinking
the first approach is the best.<br>
<br>
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<div>You can use iSCSI on ZFS to give your KVMs a a raw
block device instead of a zfs partition w/ a QCOW2
file. I've only done the zfs partition & qcow2, not
the iSCSI block. <br>
</div>
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<br>
I didn't know ZFS would provide that. Guess I've got more reading -
I wonder if it'll be faster.<br>
<br>
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cite="mid:CAEHDbACb0xCP8htsPHhA9xaBvXzGDsOv2bsBe76roQE8Rvi25Q@mail.gmail.com"
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<div>I'd do the 1st setup and get the benefits of ECC and on
the fly partitioning. I'd imagine the snapshots would be
big for either qcow or an iSCSI block. I think you'd have
to benchmark qcow vs iSCSI block to see which is faster w/
various compressions (in qcow, in ZFS, etc)</div>
<div><br>
</div>
<div>ZFS will eat up unused RAM, but Linux does that for
filesystems already so we're used to that. I don't see
any huge performance hits with modern multicore systems.</div>
<div> </div>
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<ol>
</ol>
<p>The guests will be:<br>
</p>
<p> * Both guests will be running DNS servers<br>
* One guest will be running a Postfix/Dovecot mail
server (including mailman)<br>
* The other guest will be running a LAMP stack.<br>
</p>
<p>Hints: <br>
* I don't particularly like option 2 as I'll lose
the benefits of ZFS (snapshot backups, striping, ...)<br>
* I don't know if the performance benefits of ZFS
will outweigh the overhead of KVM/libvirt.<span
class="HOEnZb"><font color="#888888"><br>
</font></span></p>
<span class="HOEnZb"><font color="#888888">
<p>--Bruce<br>
</p>
</font></span></div>
<br>
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