On 10/9/20 2:04 pm, Simon Walter wrote:
> On 2020-09-09 15:53, Brad Campbell via Dng wrote:
>>
>> It really doesn't. It'll mark a sector as "pending" (as in, I can't read
>> from it so I'll mark it for later).
>
> What does the OS get at this point? Is that a short read error?

Yep. I have some old drives here I keep around for testing :

current smart excerpt :
<snip>

196 Reallocated_Event_Count 0x0032   200   200   000    Old_age   Always       -       0
197 Current_Pending_Sector  0x0032   200   001   000    Old_age   Always       -       1
198 Offline_Uncorrectable   0x0030   200   200   000    Old_age   Offline      -       0

<snip>

SMART Self-test log structure revision number 1
Num  Test_Description    Status                  Remaining  LifeTime(hours)  LBA_of_first_error
# 1  Short offline       Completed: read failure       80%     59372         1099436031

root@test:~/smartdir# dd if=/dev/sdm bs=512 count=1 skip=1099436031
dd: error reading ‘/dev/sdm’: Input/output error
0+0 records in
0+0 records out
0 bytes (0 B) copied, 5.56285 s, 0.0 kB/s

root@test:~/smartdir# dmesg | tail -n11
[ 122.928898] sd 1:0:7:0: [sdm] tag#30 UNKNOWN(0x2003) Result: hostbyte=0x00 driverbyte=0x08 cmd_age=2s
[ 122.928974] sd 1:0:7:0: [sdm] tag#30 Sense Key : 0x3 [current]
[ 122.929035] sd 1:0:7:0: [sdm] tag#30 ASC=0x11 ASCQ=0x0
[ 122.929094] sd 1:0:7:0: [sdm] tag#30 CDB: opcode=0x28 28 00 41 88 0f f8 00 00 08 00
[ 122.929159] blk_update_request: critical medium error, dev sdm, sector 1099436024 op 0x0:(READ) flags 0x80700 phys_seg 1 prio class 0
[ 125.712897] sd 1:0:7:0: [sdm] tag#8 UNKNOWN(0x2003) Result: hostbyte=0x00 driverbyte=0x08 cmd_age=2s
[ 125.712975] sd 1:0:7:0: [sdm] tag#8 Sense Key : 0x3 [current]
[ 125.713034] sd 1:0:7:0: [sdm] tag#8 ASC=0x11 ASCQ=0x0
[ 125.713092] sd 1:0:7:0: [sdm] tag#8 CDB: opcode=0x28 28 00 41 88 0f f8 00 00 08 00
[ 125.713156] blk_update_request: critical medium error, dev sdm, sector 1099436024 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
[ 125.713229] Buffer I/O error on dev sdm, logical block 137429503, async page read

This drive just grows defects. I can zap that sector and in a couple of days it'll come up with another one.

Oddly enough, it's either unreliable electronics or flat out lying as I've zapped plenty of pending sectors on this disk :

   5 Reallocated_Sector_Ct   0x0033   200   200   140    Pre-fail  Always       -       0

> I hope I didn't make it sound like that. SMART does not include
> prediction. It's just data, and it needs be interpreted. I should have
> probably said that I have never had a drive fail without being warned by
> my monitoring system (which includes logging SMART data).

Right. Sorry, it sounded like you were relying on the SMART (Good/Bad) prediction which is notoriously terrible.
I've had drives that were practically in their death throes which SMART was quite happy to report as "Good".

On 9/9/20 11:00 pm, Hendrik Boom wrote:

> Let me wonder how the drive knows a sector is bad when it writes to it.
> Does it read it back as a check?
>

All I know is the drive will push a media error up the stack when there is a problem writing. I've never really thought about *how* it knows it's a bum write. I suppose a read-back is the only way I can think of achieving it.

Regards,
Brad