Debian11 slowness when write-caching is enabled

[Malathi]

Hi,
We are testing debian in our environment and observed that there is a significant slowness on overall system performance.
We cross-checked and confirmed that there is no issues with system hardware components. Then we noticed that disk write speed is reduced when write-caching is enabled whereas disk write speed is optimal when write-caching is disabled. Please refer the attached screenshot for details.

HDD_Write_Cahe.png (177.99 KiB) Viewed 5765 times

My questions are,
1) May i know the reason for system slowness when write-caching is enabled ?
2) Is the kernel version which we're using can cause this issue ?

OS version: Debian 11.0 Bullseye
Kernel version: 5.10.0-8-amd64

Thanks in advance.

[bw123]

...We cross-checked and confirmed that there is no issues with system hardware components.
...

How did you eliminate possible issue with hardware components? The second question is easy to answer, if you think current kernel at fault, try another kernel. I am using slightly newer 5.10.0-9-amd64 on bullseye.
I can't confirm your results using SATA SSD:

Code: Select all

# hdparm -W 0 /dev/sda

/dev/sda:
 setting drive write-caching to 0 (off)
 write-caching =  0 (off)
# dd if=/dev/zero of=/tmp/foo1.img bs=512 count=1000 oflag=dsync
1000+0 records in
1000+0 records out
512000 bytes (512 kB, 500 KiB) copied, 2.24656 s, 228 kB/s
# hdparm -W 1 /dev/sda

/dev/sda:
 setting drive write-caching to 1 (on)
 write-caching =  1 (on)
# dd if=/dev/zero of=/tmp/foo2.img bs=512 count=1000 oflag=dsync
1000+0 records in
1000+0 records out
512000 bytes (512 kB, 500 KiB) copied, 1.40418 s, 365 kB/s
# rm /tmp/foo*
# uname -r
5.10.0-9-amd64
# fdisk -l | grep model
Disk model: SanDisk SDSSDA12

FUD

[Malathi]

Thanks for the quick response,

We are having the reported issue only with SATA HDD, no performance issues found with SATA SSD so far..

How did you eliminate possible issue with hardware components?

We have our own monitoring tools to detect any hardware issue on servers

Any other suggestions other than kernel upgrade ?