Re: Slow USB3 drive (Intel amd64)

[mlelstv%serpens.de@localhost (Michael van Elst)]

mtbc%ixod.org@localhost (Mark Carroll) writes:

># time dd if=/dev/sd0 of=/dev/null bs=1m count=1k
>1024+0 records in
>1024+0 records out
>1073741824 bytes transferred in 393.518 secs (2728571 bytes/sec)
>      399.26 real         0.00 user         1.22 sys


Try /dev/rsd0.

The block device (sd0) reads through the buffer cache in small chunks.
The character device (rsd0) reads directly from the disk in large
chunks and also employs some amount of read-ahead.

Example, also from a USB3 disk:

# dd if=/dev/sd0d of=/dev/null bs=1m count=1k
1024+0 records in
1024+0 records out
1073741824 bytes transferred in 393.919 secs (2725793 bytes/sec)

# dd if=/dev/rsd0d of=/dev/null bs=1m count=1k
1024+0 records in
1024+0 records out
1073741824 bytes transferred in 11.927 secs (90026144 bytes/sec)

-- 
-- 
                                Michael van Elst
Internet: mlelstv%serpens.de@localhost
                                "A potential Snark may lurk in every tree."