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




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.