Hi there!

I'm a newbie, so don't blame me fast :)

I have few questions related to Hypervisor's local disk passthrough to VM 
strategies

Preamble: we found vmdisk hook most comfortable way to use as a "gate to local 
storage functionality" in shared clusters.
Let's assume, You have 
A. 2 or 4 TB large SSD, which You need to split on different usages: some 
diskspace provide for SQL / ETCd / Mongod etc. It must be fast, so no network 
in between. You have only one physical disk, so you can't passthrough whole of 
it to single VM. So you make LVM, and passthrough LVMs using vmdisk - this is 
how we did on some setups. 
B. 2 or 4 TB HDD for gluster bricks.

At the end, You have few VMs, which "dies" together with Hypervisor, but most 
of VMs can live migration. In together with L7 application level fail-over, it 
can lead to non-critical level services level cluster, which is not so hard to 
throw in maintenance

Yes, it does not work at real device speeds: simple dd operation with 
unpartitioned block device performs 3-4 times slower in VM, than on hypervisor. 
But, ability to mix workloads (migratable VMS with non migratable) within small 
cluster of hypervisors is more important, at some setups.

So, there are questions coming...
1. As far as I understand, there is possibility to replace vmdisk-hook vith 
cmdline. But I didn't found a way, how to get it working. I always ended with 
"Could not open '/dev/***': No such file or directory." which I could not avoid 
anyhow. May be, someone can point me to an article or other thread, where there 
are clues, how to do that?
2. what's the story behind vmdisk hook? As far as I understand from 
https://github.com/oVirt/vdsm/blob/master/vdsm.spec.in its deprecated? Why? It 
is replaced with some functionality? Why did VDSM's hook repo been deleted from 
github (in order to avoid confuse?)?
3. Is it possible to achieve with any hook or some other instrument near 
hypervisor's performance of local disk? We are ready for inconveniences like 
custom setup handling / patches and so on

Thanks in advance!

It worked in 4.3.10 / CentOS 7, but the
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