Low perfomance when read from usb flash drive

[Artyom Mirgorodsky]

> It might be a bug with your memory stick. Are your findings consistent accross 
> other brands of memory sticks aswell, between 7.1 and 8.x ?

Today, I tested another flash drive

ugen1.2: <USB 2.0> at usbus1
umass0: <BUCK> on usbus1
umass0:  SCSI over Bulk-Only; quirks = 0x0000
umass0:3:0:-1: Attached to scbus3
sg1 at umass-sim0 bus 0 target 0 lun 0
sg1: <USB 2.0 Flash Disk 1.00> Removable Direct Access SCSI-2 device 
sg1: 40.000MB/s transfers
pass1 at umass-sim0 bus 0 target 0 lun 0
pass1: <USB 2.0 Flash Disk 1.00> Removable Direct Access SCSI-2 device 
pass1: 40.000MB/s transfers
GEOM: new disk da0
da0 at umass-sim0 bus 0 target 0 lun 0
da0: <USB 2.0 Flash Disk 1.00> Removable Direct Access SCSI-2 device 
da0: 40.000MB/s transfers
da0: 3872MB (7929856 512 byte sectors: 255H 63S/T 493C)



FreeBSD-8-Current

dd if=/dev/da0 of=/dev/null bs=64k count=10000
10000+0 records in
10000+0 records out
655360000 bytes transferred in 60.320972 secs (10864546 bytes/sec)

systat -vm

Disks   ad4   ad6   da0   cd0 pass0   sg0   sg1     68560 wire
KB/t   0.00  0.00 64.00  0.00  0.00  0.00  0.00    117684 act
tps       0     0   166     0     0     0     0     75468 inact
MB/s   0.00  0.00 10.40  0.00  0.00  0.00  0.00      1860 cache
%busy     0     0    99     0     0     0     0   1136340 free



FreeBSD-7.1

dd if=/dev/da0 of=/dev/null bs=64k count=10000
10000+0 records in
10000+0 records out
655360000 bytes transferred in 44.021160 secs (14887386 bytes/sec)

systat -vm
Disks   ad4   ad6   da0
KB/t   0.00  0.00 64.00
tps       0     0   228
MB/s   0.00  0.00 14.22
%busy     0     0    99