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My PC becomes almost unusable when writing to my data drive. The main suspect which exhibits this issue is VMware Player. The problem does not happen when I myself move files in Windows Explorer or do something disk heavy in some application; it happens only after I suspend a VMware virtual machine.
As VMware Player is not writing to its save-state .vmem file itself but is delegating the task to C:\Windows\system32\ntoskrnl.exe process, then it leads me to thinking that the root cause for the issue is the OS or my PC configuration. When looking in Task Manager, I see that CPU usage is just 5..10% and memory usage is ~40%, which is normal for me. When I open Resource Monitor, I see that ntoskrnl.exe is writing intensively to the VMware .vmem file. As soon as disk writing stops, my PC immediately snaps back to normal.
I have scanned the disk for errors and performance issues with HDTune, I have tested the RAM with memtest. Everything is normal, no errors, drive performance is about 110MB/sec. I have antivirus (Avira Free) and I'm sure that ntoskrnl.exe is legitimate Windows process. Except for this issue, my PC has been running rock stable for three years.
As I understand, if OS writes to another physical internal SATA data drive, there shouldn't be any slowdowns, am I right? I wonder, if disk subsystem uses DMA to write data directly from RAM to disk, then why should it affect CPU performance and other running applications if there's plenty of RAM available? But I think, I am missing something here and maybe it's not that simple. That's why the main question is as follows:
Why writing to a hard drive affects the overall performance of a PC so much and what can I do to fix the issue?
I would like an answer which is not specific to my case but more general, to help me and other SuperUser readers understand how and why data drive performance affects overall PC performance.
Here are the specs of my PC:
CPU: Intel i3 2120
Motherboard: Gigabyte GA-H67A-USB3-B3
RAM: 8GB
Hard disks: OS and system disk - Samsung SSD 840 EVO 120 GB, connected to internal SATA3 port
Data disk (which causes the slowdowns): Seagate ST31000528AS 1000 GB, connected to internal SATA3 port
OS: Windows 7 64 bit Professional with SP1, updated regularly
JustAMartin
Posted 2014-07-11T08:52:06.780
Reputation: 1 349
the 840 EVO has a small cache of fast SLC flash and if this cache is full it needs to write the data to the slower TLC flash. Maybe this causes the delay. – magicandre1981 – 2014-07-11T14:07:40.167
I've had this issue even before I migrated my system to SSD. Still, I don't see why my PC performance is affected so badly while I'm writing to the other drive (Seagate ST31000528AS), which is not the one with Windows and applications. – JustAMartin – 2014-07-11T14:13:49.913
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analyze the disk usage with xperf/WPA: http://channel9.msdn.com/Shows/Defrag-Tools/Defrag-Tools-44-WPT-DiskIO-Analysis
– magicandre1981 – 2014-07-12T06:48:20.340Well, I already know what, why and how is using my hard disk. I just don't understand why my system gets so slow while the disk is being used, considering that Windows and all the applications are located on another, much faster SSD drive and the PC has plenty of free RAM. But thanks for the link, I'll see if that xperf provides some more clues to find out what's going on. – JustAMartin – 2014-07-12T11:40:07.627