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I have the problem, that whenever I try to run Windows within QEMU, it seems that disk access is becomming very slow after a short while. Surprisingly both access to the disk from within the VM as well as outside of the VM seems to become slow.

I have both my home and my QEMU windows drive on the same disk (this is a laptop, so I cannot use multiple disks), but on different LVM volumes (no qcow or anything, just the raw LV). Just after few minutes, windows becomes unusably slow, and the host also becomes slow. As soon as I disable the VM, the host becomes usable again. I have traced back the problem in windows to slow disk access using the resource monitor. But the problem seems to be in on the LVM side of the host. If I run iostat -xz I get the following:

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
          17,36   10,14    5,41   38,51    0,00   28,58

Device            r/s     rkB/s   rrqm/s  %rrqm r_await rareq-sz     w/s     wkB/s   wrqm/s  %wrqm w_await wareq-sz     d/s     dkB/s   drqm/s  %drqm d_await dareq-sz  aqu-sz  %util
dm-0             7,63     82,81     0,00   0,00   84,37    10,85   22,74    209,61     0,00   0,00  121,53     9,22    0,00      0,00     0,00   0,00    0,00     0,00    3,41   3,32
dm-1             0,05      0,27     0,00   0,00    5,05     5,49    0,00      0,00     0,00   0,00    0,00     0,00    0,00      0,00     0,00   0,00    0,00     0,00    0,00   0,00
dm-2             0,00      0,09     0,00   0,00    6,10    21,75    0,00      0,00     0,00   0,00    0,00     0,00    0,00      0,00     0,00   0,00    0,00     0,00    0,00   0,00
dm-3             2,28      9,12     0,00   0,00   21,28     4,00    0,00      0,00     0,00   0,00    0,00     0,00    0,00      0,00     0,00   0,00    0,00     0,00    0,05   0,53
dm-4             0,02      0,09     0,00   0,00    4,95     4,00    0,00      0,00     0,00   0,00    0,00     0,00    0,00      0,00     0,00   0,00    0,00     0,00    0,00   0,00
dm-5             0,00      0,00     0,00   0,00   31,64     4,00    0,00      0,00     0,00   0,00    0,00     0,00    0,00      0,00     0,00   0,00    0,00     0,00    0,00   0,00
dm-6             0,02      0,09     0,00   0,00    4,94     4,00    0,00      0,00     0,00   0,00    0,00     0,00    0,00      0,00     0,00   0,00    0,00     0,00    0,00   0,00
dm-7             0,00      0,09     0,00   0,00    6,85    21,75    0,00      0,00     0,00   0,00    0,00     0,00    0,00      0,00     0,00   0,00    0,00     0,00    0,00   0,00
dm-8            36,13   1454,39     0,00   0,00   46,74    40,25  528,37   2107,50     0,00   0,00  122,58     3,99    0,00      0,00     0,00   0,00    0,00     0,00   66,46  12,66
dm-9             7,63     82,77     0,00   0,00   84,49    10,85   22,74    213,86     0,00   0,00 1578,74     9,40    0,00      0,00     0,00   0,00    0,00     0,00   36,55   3,18
nvme0n1          4,49    176,13     5,82  56,45    0,19    39,26  101,54    445,00     0,07   0,07    0,95     4,38    0,00      0,00     0,00   0,00    0,00     0,00    0,07   0,38
sda             41,89   1547,29     4,19   9,10   46,21    36,93   41,60   2317,08   509,51  92,45  158,29    55,70    0,00      0,00     0,00   0,00    0,00     0,00    8,40  15,35

dm-8 is the windows LV and dm-9 is my home drive. So for some reason it seems that data is being queued for both these drives. The write speed isn't terribly fast while the system is sluggish, somewhere around 1-5MB/s at most, which is very slow for the drive I have in the system.

CPU Usage is very low, while the VM is running (both inside the VM using resource monitor, as well as on the host). Usually, it is only around 10%.

I am using Virtio as a storage adapter and I already tried different configurations (threads, caching etc), but nothing seems to change this problem.

Is there some other configuration that I could try to get a better disk access?

EDIT:

Here is the output of smartctl -a /dev/sda:

smartctl 7.0 2018-12-30 r4883 [x86_64-linux-5.4.48-gentoo-20200819] (local build)
Copyright (C) 2002-18, Bruce Allen, Christian Franke, www.smartmontools.org

=== START OF INFORMATION SECTION ===
Model Family:     Seagate FireCuda 2.5
Device Model:     ST2000LX001-1RG174
Serial Number:    ZDZ9N2W8
LU WWN Device Id: 5 000c50 0c4905536
Firmware Version: SDM1
User Capacity:    2.000.398.934.016 bytes [2,00 TB]
Sector Sizes:     512 bytes logical, 4096 bytes physical
Rotation Rate:    5400 rpm
Form Factor:      2.5 inches
Device is:        In smartctl database [for details use: -P show]
ATA Version is:   ACS-3 T13/2161-D revision 3b
SATA Version is:  SATA 3.1, 6.0 Gb/s (current: 6.0 Gb/s)
Local Time is:    Tue Sep  1 10:07:55 2020 CEST
SMART support is: Available - device has SMART capability.
SMART support is: Enabled

=== START OF READ SMART DATA SECTION ===
SMART overall-health self-assessment test result: PASSED

General SMART Values:
Offline data collection status:  (0x00) Offline data collection activity
                                        was never started.
                                        Auto Offline Data Collection: Disabled.
Self-test execution status:      (   0) The previous self-test routine completed
                                        without error or no self-test has ever 
                                        been run.
Total time to complete Offline 
data collection:                (    0) seconds.
Offline data collection
capabilities:                    (0x71) SMART execute Offline immediate.
                                        No Auto Offline data collection support.
                                        Suspend Offline collection upon new
                                        command.
                                        No Offline surface scan supported.
                                        Self-test supported.
                                        Conveyance Self-test supported.
                                        Selective Self-test supported.
SMART capabilities:            (0x0003) Saves SMART data before entering
                                        power-saving mode.
                                        Supports SMART auto save timer.
Error logging capability:        (0x01) Error logging supported.
                                        General Purpose Logging supported.
Short self-test routine 
recommended polling time:        (   1) minutes.
Extended self-test routine
recommended polling time:        ( 328) minutes.
Conveyance self-test routine
recommended polling time:        (   2) minutes.
SCT capabilities:              (0x3035) SCT Status supported.
                                        SCT Feature Control supported.
                                        SCT Data Table supported.

SMART Attributes Data Structure revision number: 10
Vendor Specific SMART Attributes with Thresholds:
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE
  1 Raw_Read_Error_Rate     0x000f   078   064   006    Pre-fail  Always       -       66205122
  3 Spin_Up_Time            0x0003   099   099   000    Pre-fail  Always       -       0
  4 Start_Stop_Count        0x0032   100   100   020    Old_age   Always       -       161
  5 Reallocated_Sector_Ct   0x0033   100   100   036    Pre-fail  Always       -       0
  7 Seek_Error_Rate         0x000f   075   060   045    Pre-fail  Always       -       29488074
  9 Power_On_Hours          0x0032   100   100   000    Old_age   Always       -       527 (193 175 0)
 10 Spin_Retry_Count        0x0013   100   100   097    Pre-fail  Always       -       0
 12 Power_Cycle_Count       0x0032   100   100   020    Old_age   Always       -       151
184 End-to-End_Error        0x0032   100   100   099    Old_age   Always       -       0
187 Reported_Uncorrect      0x0032   100   100   000    Old_age   Always       -       0
188 Command_Timeout         0x0032   100   099   000    Old_age   Always       -       4
189 High_Fly_Writes         0x003a   100   100   000    Old_age   Always       -       0
190 Airflow_Temperature_Cel 0x0022   058   048   040    Old_age   Always       -       42 (Min/Max 22/43)
191 G-Sense_Error_Rate      0x0032   100   100   000    Old_age   Always       -       1
192 Power-Off_Retract_Count 0x0032   100   100   000    Old_age   Always       -       22
193 Load_Cycle_Count        0x0032   100   100   000    Old_age   Always       -       1116
194 Temperature_Celsius     0x0022   042   052   000    Old_age   Always       -       42 (0 19 0 0 0)
197 Current_Pending_Sector  0x0012   100   100   000    Old_age   Always       -       0
198 Offline_Uncorrectable   0x0010   100   100   000    Old_age   Offline      -       0
199 UDMA_CRC_Error_Count    0x003e   200   200   000    Old_age   Always       -       0
240 Head_Flying_Hours       0x0000   100   253   000    Old_age   Offline      -       523h+48m+09.290s
241 Total_LBAs_Written      0x0000   100   253   000    Old_age   Offline      -       2770583284
242 Total_LBAs_Read         0x0000   100   253   000    Old_age   Offline      -       713825407
254 Free_Fall_Sensor        0x0032   100   100   000    Old_age   Always       -       0

SMART Error Log Version: 1
No Errors Logged

SMART Self-test log structure revision number 1
Num  Test_Description    Status                  Remaining  LifeTime(hours)  LBA_of_first_error
# 1  Short offline       Completed without error       00%       523         -

SMART Selective self-test log data structure revision number 1
 SPAN  MIN_LBA  MAX_LBA  CURRENT_TEST_STATUS
    1        0        0  Not_testing
    2        0        0  Not_testing
    3        0        0  Not_testing
    4        0        0  Not_testing
    5        0        0  Not_testing
Selective self-test flags (0x0):
  After scanning selected spans, do NOT read-scan remainder of disk.
If Selective self-test is pending on power-up, resume after 0 minute delay.
  • Your hard drive is probably failing. Check it. e.g. with smartctl -a /dev/sda. – Michael Hampton Aug 31 at 15:13
  • @MichaelHampton Thank you for the hint. The drive is brand new (about 1month old), but some smart attributes report pre-fail and old-age. Guess this should teach me to also check new hardware and not assume I actually get what I ordered from the vendor. I hope I can get a replacement. – LiKao Aug 31 at 15:20
  • Eh? All of the attributes will say pre-fail or old age. That is the category they fall into. Whether they have failed or are failing is something different. You should post the output here and let a few extra sets of eyes look at it. – Michael Hampton Aug 31 at 15:25
  • @MichaelHampton Argh, never mind. You are right. I am too tired after fighting with this non-responding VM for some time today... I will post the output as soon as I got some rest. – LiKao Aug 31 at 15:26
  • @MichaelHampton Added output from smartctl. Now that I had a good night sleep, everything seems fine to me. But maybe someone else can spot something. – LiKao Sep 1 at 8:11

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