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Where am I hitting the invisible SD card cache?
2019 Community Moderator ElectionOptimal Linux Distro to Install to SD card to use as USB-Bootloader for PC?Linux support for new Sony Vaio Z external graphics card?Udev triggers are not firing on insert of CF card into USB card reader (anymore)Mount an SD card over USB?Set PERM_WRITE_PROTECT on an SD cardReduce cache size of flash storage deviceswhat's the difference between page cache and buffer cache?How to know which user agent is hitting my server?Where to set kernelns buffer/cache sizeWhere does kernel define the SD card naming index?
I'm trying to clear an SD card connected via a USB dongle.
Here's what I do:
# dd if=/dev/zero of=/dev/sdb bs=$((1024*4))
dd: error writing '/dev/sdb': No space left on device
1002267+0 records in
1002266+0 records out
4105281536 bytes (4.1 GB, 3.8 GiB) copied, 2.10549 s, 1.9 GB/s
The weird things I see are: This is an SD HC I card, so the transfer should never reach 1.9GB/s. The card is 16GB and correctly reports as such in dmesg.
Ok, let's check it's written:
# head -c 4105281536 /dev/zero | sha1sum
a1750724bfbf0ada57d986f16b26e789a6c61a1d -
(reverse-i-search)`': ^C
# head -c 4105281536 /dev/sdb | sha1sum
a1750724bfbf0ada57d986f16b26e789a6c61a1d -
Seems ok. But when I plug is out and in again, it magically has the same filesystem available as before.
When I mount them and change the files, the modification is also persisted, even though the sha1sum still shows it as zeros.
The device is definitely /dev/sdb:
[ 9895.437518] scsi 4:0:0:0: Direct-Access Mass Storage Device PQ: 0 ANSI: 0 CCS
[ 9895.439248] sd 4:0:0:0: [sdb] 30318592 512-byte logical blocks: (15.5 GB/14.5 GiB)
[ 9895.439398] sd 4:0:0:0: [sdb] Write Protect is off
[ 9895.439404] sd 4:0:0:0: [sdb] Mode Sense: 03 00 00 00
[ 9895.439557] sd 4:0:0:0: [sdb] No Caching mode page found
[ 9895.439564] sd 4:0:0:0: [sdb] Assuming drive cache: write through
[ 9895.441922] sdb: sdb1 sdb2
[ 9895.443517] sd 4:0:0:0: [sdb] Attached SCSI removable disk
What's happening here?
Running on kernel 4.20.3.
linux usb removable-storage
asked 20 hours ago
viraptorviraptor
1927
add a comment |
I'm trying to clear an SD card connected via a USB dongle.
Here's what I do:
# dd if=/dev/zero of=/dev/sdb bs=$((1024*4))
dd: error writing '/dev/sdb': No space left on device
1002267+0 records in
1002266+0 records out
4105281536 bytes (4.1 GB, 3.8 GiB) copied, 2.10549 s, 1.9 GB/s
The weird things I see are: This is an SD HC I card, so the transfer should never reach 1.9GB/s. The card is 16GB and correctly reports as such in dmesg.
Ok, let's check it's written:
# head -c 4105281536 /dev/zero | sha1sum
a1750724bfbf0ada57d986f16b26e789a6c61a1d -
(reverse-i-search)`': ^C
# head -c 4105281536 /dev/sdb | sha1sum
a1750724bfbf0ada57d986f16b26e789a6c61a1d -
Seems ok. But when I plug is out and in again, it magically has the same filesystem available as before.
When I mount them and change the files, the modification is also persisted, even though the sha1sum still shows it as zeros.
The device is definitely /dev/sdb:
[ 9895.437518] scsi 4:0:0:0: Direct-Access Mass Storage Device PQ: 0 ANSI: 0 CCS
[ 9895.439248] sd 4:0:0:0: [sdb] 30318592 512-byte logical blocks: (15.5 GB/14.5 GiB)
[ 9895.439398] sd 4:0:0:0: [sdb] Write Protect is off
[ 9895.439404] sd 4:0:0:0: [sdb] Mode Sense: 03 00 00 00
[ 9895.439557] sd 4:0:0:0: [sdb] No Caching mode page found
[ 9895.439564] sd 4:0:0:0: [sdb] Assuming drive cache: write through
[ 9895.441922] sdb: sdb1 sdb2
[ 9895.443517] sd 4:0:0:0: [sdb] Attached SCSI removable disk
What's happening here?
Running on kernel 4.20.3.
linux usb removable-storage
asked 20 hours ago
viraptorviraptor
1927
add a comment |
I'm trying to clear an SD card connected via a USB dongle.
Here's what I do:
# dd if=/dev/zero of=/dev/sdb bs=$((1024*4))
dd: error writing '/dev/sdb': No space left on device
1002267+0 records in
1002266+0 records out
4105281536 bytes (4.1 GB, 3.8 GiB) copied, 2.10549 s, 1.9 GB/s
The weird things I see are: This is an SD HC I card, so the transfer should never reach 1.9GB/s. The card is 16GB and correctly reports as such in dmesg.
Ok, let's check it's written:
# head -c 4105281536 /dev/zero | sha1sum
a1750724bfbf0ada57d986f16b26e789a6c61a1d -
(reverse-i-search)`': ^C
# head -c 4105281536 /dev/sdb | sha1sum
a1750724bfbf0ada57d986f16b26e789a6c61a1d -
Seems ok. But when I plug is out and in again, it magically has the same filesystem available as before.
When I mount them and change the files, the modification is also persisted, even though the sha1sum still shows it as zeros.
The device is definitely /dev/sdb:
[ 9895.437518] scsi 4:0:0:0: Direct-Access Mass Storage Device PQ: 0 ANSI: 0 CCS
[ 9895.439248] sd 4:0:0:0: [sdb] 30318592 512-byte logical blocks: (15.5 GB/14.5 GiB)
[ 9895.439398] sd 4:0:0:0: [sdb] Write Protect is off
[ 9895.439404] sd 4:0:0:0: [sdb] Mode Sense: 03 00 00 00
[ 9895.439557] sd 4:0:0:0: [sdb] No Caching mode page found
[ 9895.439564] sd 4:0:0:0: [sdb] Assuming drive cache: write through
[ 9895.441922] sdb: sdb1 sdb2
[ 9895.443517] sd 4:0:0:0: [sdb] Attached SCSI removable disk
What's happening here?
Running on kernel 4.20.3.
linux usb removable-storage
asked 20 hours ago
viraptorviraptor
1927
I'm trying to clear an SD card connected via a USB dongle.
Here's what I do:
# dd if=/dev/zero of=/dev/sdb bs=$((1024*4))
dd: error writing '/dev/sdb': No space left on device
1002267+0 records in
1002266+0 records out
4105281536 bytes (4.1 GB, 3.8 GiB) copied, 2.10549 s, 1.9 GB/s
The weird things I see are: This is an SD HC I card, so the transfer should never reach 1.9GB/s. The card is 16GB and correctly reports as such in dmesg.
Ok, let's check it's written:
# head -c 4105281536 /dev/zero | sha1sum
a1750724bfbf0ada57d986f16b26e789a6c61a1d -
(reverse-i-search)`': ^C
# head -c 4105281536 /dev/sdb | sha1sum
a1750724bfbf0ada57d986f16b26e789a6c61a1d -
Seems ok. But when I plug is out and in again, it magically has the same filesystem available as before.
When I mount them and change the files, the modification is also persisted, even though the sha1sum still shows it as zeros.
The device is definitely /dev/sdb:
[ 9895.437518] scsi 4:0:0:0: Direct-Access Mass Storage Device PQ: 0 ANSI: 0 CCS
[ 9895.439248] sd 4:0:0:0: [sdb] 30318592 512-byte logical blocks: (15.5 GB/14.5 GiB)
[ 9895.439398] sd 4:0:0:0: [sdb] Write Protect is off
[ 9895.439404] sd 4:0:0:0: [sdb] Mode Sense: 03 00 00 00
[ 9895.439557] sd 4:0:0:0: [sdb] No Caching mode page found
[ 9895.439564] sd 4:0:0:0: [sdb] Assuming drive cache: write through
[ 9895.441922] sdb: sdb1 sdb2
[ 9895.443517] sd 4:0:0:0: [sdb] Attached SCSI removable disk
What's happening here?
Running on kernel 4.20.3.
linux usb removable-storage
linux usb removable-storage
asked 20 hours ago
viraptorviraptor
1927
asked 20 hours ago
viraptorviraptor
1927
asked 20 hours ago
viraptorviraptor
1927
asked 20 hours ago
viraptorviraptor
1927
asked 20 hours ago
viraptorviraptor
1927
1927
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
I notice dd it only copies 3.8 GiB when the drive is 14.5 GiB. So what you're writing to is most likely not the sd card. Unplug the SD card and then check ls -lh /dev/sdb.
I suspect you have accidentally created a regular file on /dev called /dev/sdb. Since /dev is a ram disk it explains why you can write to it at 2GBps
When you've finished your dd command, remember to sync just in case. This will tell the kernel to flush any cache it has.
answered 16 hours ago
Philip CoulingPhilip Couling
1,964920
add a comment |
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1 Answer
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1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
I notice dd it only copies 3.8 GiB when the drive is 14.5 GiB. So what you're writing to is most likely not the sd card. Unplug the SD card and then check ls -lh /dev/sdb.
I suspect you have accidentally created a regular file on /dev called /dev/sdb. Since /dev is a ram disk it explains why you can write to it at 2GBps
When you've finished your dd command, remember to sync just in case. This will tell the kernel to flush any cache it has.
answered 16 hours ago
Philip CoulingPhilip Couling
1,964920
add a comment |
I notice dd it only copies 3.8 GiB when the drive is 14.5 GiB. So what you're writing to is most likely not the sd card. Unplug the SD card and then check ls -lh /dev/sdb.
I suspect you have accidentally created a regular file on /dev called /dev/sdb. Since /dev is a ram disk it explains why you can write to it at 2GBps
When you've finished your dd command, remember to sync just in case. This will tell the kernel to flush any cache it has.
answered 16 hours ago
Philip CoulingPhilip Couling
1,964920
add a comment |
I notice dd it only copies 3.8 GiB when the drive is 14.5 GiB. So what you're writing to is most likely not the sd card. Unplug the SD card and then check ls -lh /dev/sdb.
I suspect you have accidentally created a regular file on /dev called /dev/sdb. Since /dev is a ram disk it explains why you can write to it at 2GBps
When you've finished your dd command, remember to sync just in case. This will tell the kernel to flush any cache it has.
answered 16 hours ago
Philip CoulingPhilip Couling
1,964920
I notice dd it only copies 3.8 GiB when the drive is 14.5 GiB. So what you're writing to is most likely not the sd card. Unplug the SD card and then check ls -lh /dev/sdb.
I suspect you have accidentally created a regular file on /dev called /dev/sdb. Since /dev is a ram disk it explains why you can write to it at 2GBps
When you've finished your dd command, remember to sync just in case. This will tell the kernel to flush any cache it has.
answered 16 hours ago
Philip CoulingPhilip Couling
1,964920
answered 16 hours ago
Philip CoulingPhilip Couling
1,964920
answered 16 hours ago
Philip CoulingPhilip Couling
1,964920
answered 16 hours ago
Philip CoulingPhilip Couling
1,964920
1,964920
add a comment |
add a comment |
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