Comments on: Test read/write speed of usb and ssd drives with dd command on Linux

By: kokozcal

kokozcal — Fri, 04 Mar 2022 05:13:51 +0000

Usb 3:

dd if=/dev/zero of=largefile bs=8k count=10000
10000+0 records in
10000+0 records out
81920000 bytes (82 MB, 78 MiB) copied, 0.0344905 s, 2.4 GB/s

Bus 004 Device 002: ID 0781:5583 SanDisk Corp. Ultra Fit

By: hjs

hjs — Sat, 03 Jun 2017 21:33:47 +0000

anon@nux-16:/home/home$ sudo dd if=/dev/zero of=./largefile bs=1M count=1024
[sudo] password for anon:
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 0.989448 s, 1.1 GB/s

how is this possible?

By: Stephen Lynx

Stephen Lynx — Fri, 24 Mar 2017 19:19:44 +0000

dd if=/dev/zero of=./largefile bs=1M count=1024 is just writing to ram, tho.

By: dega

dega — Sun, 22 Jan 2017 20:50:45 +0000

Nice post!
On my machine (distro: Mageia), pendrives are cached by kernel.
So, a simple dd do not measure the real write speed (dd reports 63MB/s).
So I disabled the cache with the sync option of mount.
dd now reports 170 KB/s (big difference)

Looking at your write speed results, I suspect that your pendrive is also cached by the kernel.

By: mrh

mrh — Wed, 24 Jun 2015 14:44:00 +0000

if dd command is used to monitor performance of a drive especially for a usb disk, conv=fsync should be set in order to flush the memory each time during the write operation.

By: Ger

Ger — Sun, 10 Aug 2014 11:49:00 +0000

sudo hdparm -t /dev/sdxx is far safer than dd which I would never recommend anyone run to benchmark a drive ever