virtualbox.org

Hello,

On my Linux PC there is an SSHD. So this is a combination of an integrated SSD in a HD (Hybrid). The SSD is automatic used to fasten the system. So when I boot my Linux it is much faster because the data that is often used is saved automatically in the SSD section.

So my question is:
When I boot Windows as guest as virtual machine: Does this also cash data in the SSD section?

I would not appreciate if this would be so. Because the it would always change the data in the SSD cach between the data used for Virtual Windows boot and the data for Linux boot.

Would appreciate some answer. Thank you.

A quick Google on how SSHDs provision the SSD part shows that usually the drive decides for itself what gets mirrored for faster reading from the SSD part. Occasionally a host OS can decide what gets mirrored on the SSD part.

To the best of my knowledge, having perused the Virtualbox manual, I see nothing to indicate Virtualbox has any knowledge that the host disk even is an SSHD, let alone how to influence the data-mirroring.

The easiest way to check on this is to search the PDF manual that is in your Virtualbox installation folder for 'SSHD'. My search returned no results.

I would suppose that a good SSHD would not mirror data until it becomes commonly used. Replacing old data with new-but-not-commonly-read data would defeat the purpose of the SSD part.

I believe that Virtualbox has no control over the mirroring function of the SSHD.

AFAICS this is probably a standard caching feature. Operating Systems have been doing this using HDD and RAM since forever.

I don't see why SSD+HDD should require a huge concept change, except that it's done at the sector level, by the hardware. And the latter has no concept that some sectors belong to a VDI and while others do not.

Also there's no need for VirtualBox to duplicate functionality that the host hardware already takes care of.

@scottgus1 and @mpack thank you.

AFAICS this is probably a standard caching feature. Operating Systems have been doing this using HDD and RAM since forever.

Do I understand right, that you assume, that the fast virtual machine booting that I observed has nothing to do with the SSD part of the SSHD. Are you trying to say that the virtual machine fast booting during the same Linux session might be related to the fact that parts of the boot process were still stored in RAM?

-> I need to take a closer look at whether the first boot in a Linux session is slower than the following ones.

What do you mean with "concept change" in

I don't see why SSD+HDD should require a huge concept change, ...

Do you mean "You do not see a reason for a change of data in the SSD cach between the data used for Virtual Windows boot and the data for Linux boot." ?

The fast(er) booting you observed can be related to the SSD caching inside your SSHD.
BUT: You cannot influence what the SSHD is chaching so it is just coincidence if it happens to speed up some guest tasks.
The SSHD has some unknown internel algorithm to decide which data blocks are put into the cache or not.

Martin wrote: BUT: You cannot influence what the SSHD is chaching so it is just coincidence if it happens to speed up some guest tasks.

Correct. And, since a VDI file is just a file on the host drive, like any other host app file, we don't need to take special measures to ensure that often-used sectors in a VDI are cached by the host SSD.