On Sat, Jan 16, 2010 at 01:44:49AM +0100, T. Tofus von Blisstein wrote:
> Hello,
>
> I have noticed that writing to a usb drive is "slow".
>
> What does "slow" mean?
>
> It means that compared to other OS's.
>
> Which OS's?
>
> Yes, it hurts: the penguin.
Hello there,
I came across a cheap USB flash drive, particularly a SanDisk Cruzer U3:
umass0 at uhub1 port 1 configuration 1 interface 0 "SanDisk SanDisk Cruzer" rev
2.00/2.00 addr 2
umass0: using SCSI over Bulk-Only
scsibus3 at umass0: 2 targets, initiator 0
sd1 at scsibus3 targ 1 lun 0: <SanDisk, SanDisk Cruzer, 8.02> SCSI0 0/direct
removable
sd1: 3863MB, 512 bytes/sec, 7913471 sec total
Reading and writing from/to a raw disk "/dev/rsd1c" gives same exact
rates as on other OSes:
$ sudo dd if=/dev/rsd1c of=/dev/null bs=128k count=1600
1600+0 records in
1600+0 records out
209715200 bytes transferred in 8.822 secs (23771541 bytes/sec)
$ sudo dd if=/dev/zero of=/dev/rsd1c bs=128k count=1600
1600+0 records in
1600+0 records out
209715200 bytes transferred in 19.253 secs (10892315 bytes/sec)
Which are reasonable numbers.
Now let's put a filesystem on it:
$ sudo fdisk -i sd1
Do you wish to write new MBR and partition table? [n] y
Writing MBR at offset 0.
$ sudo disklabel -E sd1
Label editor (enter '?' for help at any prompt)
> a
partition: [a]
offset: [63]
size: [7903917]
FS type: [4.2BSD]
> w
> q
No label changes.
$ sudo newfs sd1a
/dev/rsd1a: 3859.3MB in 7903916 sectors of 512 bytes
20 cylinder groups of 202.47MB, 12958 blocks, 25984 inodes each
super-block backups (for fsck -b #) at:
32, 414688, 829344, 1244000, 1658656, 2073312, 2487968, 2902624, 3317280,
3731936, 4146592,
4561248, 4975904, 5390560, 5805216, 6219872, 6634528, 7049184, 7463840,
7878496,
$ sudo mount /dev/sd1a /mnt/test; cd /mnt/test
$ sudo dd if=/dev/zero of=./x bs=128k count=1600
1600+0 records in
1600+0 records out
209715200 bytes transferred in 254.224 secs (824923 bytes/sec)
(confirmed that pengingwrites is 0 right after dd exits with systat
iostat)
As you can see here, 800KB/s is quite low, compared to raw read rate.
What can be the cause? I don't know, but let's try formatting sd1a with
frag-size of 8192 and block-size of 65536
...
(same exact sequence of steps as above, just adjust frag-size and
block-size)
...
$ time (sudo dd if=/dev/zero of=./x bs=128k count=3200; sync)
3200+0 records in
3200+0 records out
419430400 bytes transferred in 21.194 secs (19789417 bytes/sec)
0m42.44s real 0m0.00s user 0m0.33s syste
419430400/42.44=9,882,902.92 That's almost 10MB/s
Perhaps people who are having problems with their "slow" USB flash
drives can try the same experiment, see if it helps.
