VDI disk disappears from guest Windows Server 2008 R2 during active writing/reading

[sodeistvie26]

I have a host system:
System uname: Linux-4.4.9-x86_64-Intel-R-_Core-TM-_i3-6100_CPU_@_3.70GHz-with-gentoo-2.2
KiB Mem: 16320000 total, 95200 free
KiB Swap: 54525944 total, 54505032 free

And VirtualBox on it:
VirtualBox 5.0.20r106931

My Guest System is:
Name: win2008r2
Guest OS: Windows 2008 (64-bit)
Memory size: 8192MB
Paravirt. Provider: HyperV
Storage Controller Name (0): SATA
Storage Controller Type (0): IntelAhci
Storage Controller Instance Number (0): 0
Storage Controller Max Port Count (0): 30
Storage Controller Port Count (0): 6
Storage Controller Bootable (0): on
SATA (0, 0): Empty
SATA (1, 0): /var/lib/virtualbox/machines/win2008r2/Snapshots/{71b7ff1d-2b5e-47d2-ba91-74d9a3aae4eb}.vdi (UUID: 71b7ff1d-2b5e-47d2-ba91-74d9a3aae4eb)
SATA (2, 0): /var/lib/virtualbox/machines/win2008r2/win2008r2-disk1.vdi (UUID: 834e8637-0e9a-44fe-9303-b38cb2c58c1d)
SATA (3, 0): /mnt/1cdb/1c77.vdi (UUID: 9922bb56-b690-4455-944a-5783d46ff03a)
SATA (5, 0): /mnt/1cdb/1c83.vdi (UUID: f6e50680-1f67-4f4d-9f30-b831bd9f568f)

1с77.vdi and 1c83.vdi are located on ssd

SSD is:
=== START OF INFORMATION SECTION ===
Device Model: INTEL SSDSC2BW120H6
Serial Number: CVTR529306BH120AGN
LU WWN Device Id: 5 5cd2e4 14c8ee241
Firmware Version: RG21
User Capacity: 120,034,123,776 bytes [120 GB]
Sector Size: 512 bytes logical/physical
Rotation Rate: Solid State Device
Device is: Not in smartctl database [for details use: -P showall]
ATA Version is: ACS-3 (minor revision not indicated)
SATA Version is: SATA 3.2, 6.0 Gb/s (current: 6.0 Gb/s)
Local Time is: Wed Jun 27 09:39:11 2018 MSK
SMART support is: Available - device has SMART capability.
SMART support is: Enabled

When users in Guest OS make copying or reading operations with 1c77.vdi or 1c83.vdi, the disks disappear from the guest system and all programs which working with it are crashing. What is the reason for this behavior?

[mpack]

Please provide a VM log file. With the VM fully shut down, right click it in the GUI. Select "Show Log" and save "VBox.log" (no other file) to a zip file. Attach the zip here.

[sodeistvie26]

Please provide a VM log file. With the VM fully shut down, right click it in the GUI. Select "Show Log" and save "VBox.log" (no other file) to a zip file. Attach the zip here.

I haven't got GUI, only vboxmanage utility. Folder with logs is empty. Where to find the folder with logs in the configuration file?

[socratis]

In your VM directory, there's a "Logs" subdirectory. ZIP the "VBox.log" (only) and attach it.

[sodeistvie26]

In your VM directory, there's a "Logs" subdirectory. ZIP the "VBox.log" (only) and attach it.

[socratis]

VirtualBox VM 5.0.20 r106931 linux.amd64 (Apr 28 2016 15:31:30) release log

That's a more than 2 year old version. You should update to the latest one. And don't forget the matching Extension Pack.

00:00:00.734335 NumCPUs <integer> = 0x0000000000000002 (2)
00:00:00.862104 CPUM: Physical host cores: 2
00:00:00.862456 Full Name: "Intel(R) Core(TM) i3-6100 CPU @ 3.70GHz"

You have assigned all your CPUs to the VM. The host is going to run low on resources, since VirtualBox cares about physical processors (cores), not logical ones (threads). Your i3-6100 has 2 cores, not 4.

00:00:00.734511 ICH9 <integer> = 0x0000000000000001 (1)

Any particular reason why you chose an unsupported, warning-laden, specific-guest-only chipset? Please change it back to the default PIIX3!

00:00:00.734431 [/Devices/ahci/0/LUN#1/AttachedDriver/Config/Parent/Parent/Parent/Parent/Parent/] (level 11)

Do not keep that many snapshots, it's a recipe for disaster. Consolidate them.

00:00:00.715477 File system of '/mnt/1cdb/1c77.vdi' is btrfs
00:00:00.716428 File system of '/mnt/1cdb/1c83.vdi' is btrfs

That may answer your own question. The files are not local and you don't know what's happening in between working and failing. I suggest that you look in the 'dmesg' of the host and see if you can find any clues...