Why do we want to connect hyper-v vm to a physical hard drive?

Castlewood
Castlewood used Ask the Experts™
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I'm new to this job.
We have a file server with all network shared drives. That server is a vm in a single hyper-v host with cluster. And the storage is local -- no SAN, etc.
I noticed this vm has two hard drives connected:
1. IDE Controller 0 : hard drive servername.vhdx
2. ScSI Controller:   Hard Drive: Physical drive Disk 6 7448.00 GB Bus 0 Lun 1 Target 0

Can you tell me if there is specific reason we want to connect to the physical hard drive instead of using virtual drives?
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It was maybe added for more additional hard drive space. Is your local data store almost out of space? At the time it could of been the cheapest solution without buying a NAS or SAN.
Philip ElderTechnical Architect - HA/Compute/Storage

Commented:
"single hyper-v host with cluster". That doesn't really make any sense?

Is the host standalone or a node in a Hyper-V cluster?

The 7TB drive is connected via USB and is being passed through to the guest VM?
I'm not sure what version of Hyper-V you have but what you describe is called a pass-through disk.

If it's prior to 2012, VHDs had a limit of 2TB and you have almost 7.5 TB on  that which may be why.

In addition pass-through disks before had higher performance than virtual disks. Perhaps, it's to give the file server exclusive use of the hard disk.
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Author

Commented:
"with cluster" is a type. Sorry, should be "without cluster"
Ross, we are on 2012 R2 Hyper-V so 2T limit should not be the reason why we want to use 7.5T on pass-through. Since that particular vm is for network shared drives/files by whole company I guess could it be because pass-through to a physical hd is more flexible, speedy, and allowed bigger capacity??

Another question is, once that particular physical drive is used by a vm via pass-through, that drive can NOT be available as pass-through to other vm, correct?
Technical Architect - HA/Compute/Storage
Commented:
All of our standalone hosts are configured with two logical disks on one RAID 6 array:
+ LD0: 75GB Host OS
+ LD1: ???GB/??TB Data for VHDX and Config Files

We have standalone hosts with as little as 4 3.5" 15K SAS disks to 24 2.5" 10K or NearLine 7200 RPM disks.

In 2012 R2 pass-through is discouraged. Performance of VHDX on the above configured array with 8x 10K SAS in RAID 6 is about 800MB/Second and ~250-400 IOPS per disk depending on block size through the formatted stack.

How is that pass-through disk backed up?
That right, a pass through disk can't be made available to another VM once assigned.

The performance of pass through disks vs using vhdx is negligble. It's less flexible since now you can't put other virtual disks on it.  

It was probably thought as a dedicated file storage and nothing else hence why it might have just been put as pass-through. There's really no other good reason to do otherwise.

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