VirtualBox

Changes between Version 3 and Version 4 of Ticket #8311, comment 15


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Timestamp:
11/13/2019 03:13:08 AM (8 months ago)
Author:
hwertz
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  • Ticket #8311, comment 15

    v3 v4  
    11I've found a usable workaround to be switching my disks in VirtualBox to IDE.  The virtual IDE "can" still time out, but IDE's multisector read and write mode max at like 16 sectors (8KB), or maybe 256 sectors (128KB), versus SATA allowing for 64MB or more via larger transfers and native command queueing; that's 1/512th the data in that queue.  In days of yore, SATA gave a massive speed increase in VMs compared to IDE (the 8KB transfers plus mucking about with I/O ports meant a lot of virtualization overhead); with VT-X flipped on the difference is low enough; I haven't run some synthetic disk I/O benchmark but in real use I can't tell the difference in terms of speed or CPU usage.  If my physical disk I/O is nice, the IDE runs nice; if the disk I/O is slow, the OS in the virtual box (Linux or Windows) simply run through their read and write queues pretty slowly, rather than spitting out large 64MB requests then timing out. 
     2 
     3Root cause is the Linux write cache (on the host) becoming quite large, then disk I/O is quite slow during the time that cache flushes out.  If any disk I/O from a VirtualBox takes over ~15 seconds, the Linux or Windows OS in the virtual machine assumes the SATA drive failed and counts it as a read or write error. 
    24 
    35For a Linux VM, you just add the IDE controller, remove your disk (and CD if you want) from SATA and add them onto IDE. Remove the SATA controller if you want.  Done.   

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