Re: DD bs=4M option on USB mem-stick creates false format

[Pascal Hambourg <pascal@plouf.fr.eu.org>]

Le 27/03/2017 à 20:11, David Christensen a écrit :
> For example, here is an ADATA 4 marketing-GB USB flash drive:
(...)
> Burning 10 MB using 'bs=1M':
>
> 2017-03-27 11:01:23 root@jesse ~
> # time dd if=/dev/urandom of=/dev/sdb seek=3000 count=10 bs=1M && sync
> 10+0 records in
> 10+0 records out
> 10485760 bytes (10 MB) copied, 2.93679 s, 3.6 MB/s
>
> real    0m2.941s
> user    0m0.000s
> sys    0m1.020s
>
>
> Burning 10 MB using default bs:
>
> 2017-03-27 11:01:57 root@jesse ~
> # time dd if=/dev/urandom of=/dev/sdb seek=6144000 count=20480 && sync
> 20480+0 records in
> 20480+0 records out
> 10485760 bytes (10 MB) copied, 5.38085 s, 1.9 MB/s
>
> real    0m5.385s
> user    0m0.012s
> sys    0m1.388s

This is not specific to write operation on flash devices.
Default 512-byte block size has also consistently shown degraded 
performance in read and write operation on hard disk drives.