KVM vs ZFS

Tom Buskey tom at buskey.name
Mon Aug 24 10:15:54 EDT 2015


On Fri, Aug 21, 2015 at 5:47 PM, Bruce Dawson <jbd at codemeta.com> wrote:

> On 08/21/2015 05:30 PM, Tom Buskey wrote:
>
>
>
> On Fri, Aug 21, 2015 at 3:33 PM, Bruce Dawson <jbd at codemeta.com> wrote:
>
>> For this rainy weekend, please consider the following:
>>
>> 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.
>>
>>
> 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.
>
>
> 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.
>

You *can* setup the zpool to make 2 copies (copies=2) inside a single
device.  However, if the hardware fails, you lose data.  The usual zpool
setups are mirror or a raidz across multiple devices. raidz is similar to
RAID5 w/o the write hole.


> 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.
>
>
> I didn't know ZFS would provide that. Guess I've got more reading - I
> wonder if it'll be faster.
>

I know it is in Solaris.  I've head of others doing it in BSD.  I've not
done it in Linux yet.  Linux hasn't solidified iSCSI target/initiators like
the others.
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