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[Discuss] linux on usb stick

Bill Bogstad wrote:
> Recent? versions of VirtualBox have an option to control "host io caching".
> Their documentation states that VirtualBox uses its own "small cache"
> to buffer writes even
> if you turn off "host io caching".   No idea what that means.

"Host I/O caching" is the host's I/O cache. On Unix it's the kernel I/O 
buffers used for async mounts. On Windows it's the write policies for 
disk devices.

VirtualBox can't actually turn off a host's I/O cache. All it can do is 
issue fsync or FlushFileBuffers calls against VM container files upon 
request from guests. There is still some host-level cache involved 
between when the guest finishes writing and issues the flush call and 
when the host can act upon VirtualBox's flush call.

VirtualBox may have its own supplemental write cache that cannot be 
disabled. I don't know for sure and I don't really care. I finally gave 
up on VirtualBox a couple of years ago after a Linux guest crashed the 
hypervisor which in turn crashed the Linux host.

Rich P.

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