Re: Re: Re: BUG in kernel: Wrong Handling of USB HDD’s in scsiglue(slave_configure) and scsi/sd(sd_read_cache_type)

Amit Sahrawat
2011-10-07T05:09:45Z

Trying to set the cache type as "write back" through "echo "write
back" > /sys/class/scsi_disk/<disk>/cache_type" does not work.
Few logs :
#> usb 2-1.4: new high speed USB device using ehci-sdp and address 5
usb 2-1.4: New USB device found, idVendor=152d, idProduct=2339
usb 2-1.4: New USB device strings: Mfr=1, Product=2, SerialNumber=5
usb 2-1.4: Product: USB to ATA/ATAPI Bridge
usb 2-1.4: Manufacturer: JMicron
usb 2-1.4: SerialNumber: 3446184AA01C
scsi1 : usb-storage 2-1.4:1.0
scsi 1:0:0:0: Direct-Access SAMSUNG HM501IX PQ: 0 ANSI: 2 CCS
sd 1:0:0:0: [sda] 976773168 512-byte logical blocks: (500 GB/465 GiB)
sd 1:0:0:0: [sda] Write Protect is off
sd 1:0:0:0: [sda] Write cache: disabled, read cache: enabled, doesn't
support DPO or FUA
sda:

#> echo "write back" > /sys/class/scsi_disk/1\:0\:0\:0/cache_type
sd 1:0:0:0: [sda] Sense Key : 0x5 [current]
sd 1:0:0:0: [sda] ASC=0x20 ASCQ=0x0

#> usb 2-1.4: new high speed USB device using ehci-sdp and address 4
usb 2-1.4: New USB device found, idVendor=0bc2, idProduct=2300
usb 2-1.4: New USB device strings: Mfr=1, Product=2, SerialNumber=3
usb 2-1.4: Product: Portable
usb 2-1.4: Manufacturer: Seagate
usb 2-1.4: SerialNumber: 2GHW02GR
scsi0 : usb-storage 2-1.4:1.0

#>
#> scsi 0:0:0:0: Direct-Access Seagate Portable 0130 PQ: 0 ANSI: 4
sd 0:0:0:0: [sda] 488397168 512-byte logical blocks: (250 GB/232 GiB)
sd 0:0:0:0: [sda] Write Protect is off
sd 0:0:0:0: [sda] No Caching mode page present
sd 0:0:0:0: [sda] Assuming drive cache: write through
sd 0:0:0:0: [sda] No Caching mode page present
sd 0:0:0:0: [sda] Assuming drive cache: write through
sda: sda1 sda2 sda3 sda4
sd 0:0:0:0: [sda] No Caching mode page present
sd 0:0:0:0: [sda] Assuming drive cache: write through
sd 0:0:0:0: [sda] Attached SCSI disk

#> echo "write back" > /sys/class/scsi_disk/0\:0\:0\:0/cache_type
sd 0:0:0:0: [sda] No Caching mode page present
sd 0:0:0:0: [sda] Assuming drive cache: write through
#>

#> usb 2-1.4: new high speed USB device using ehci-sdp and address 7
usb 2-1.4: New USB device found, idVendor=1058, idProduct=070a
usb 2-1.4: New USB device strings: Mfr=1, Product=2, SerialNumber=3
usb 2-1.4: Product: My Passport 070A
usb 2-1.4: Manufacturer: Western Digital
usb 2-1.4: SerialNumber: 575832314132304534373635
scsi3 : usb-storage 2-1.4:1.0
scsi 3:0:0:0: Direct-Access WD My Passport 070A 1032 PQ: 0 ANSI: 4
scsi 3:0:0:1: CD-ROM WD Virtual CD 070A 1032 PQ: 0 ANSI: 4
scsi 3:0:0:2: Enclosure WD SES Device 1032 PQ: 0 ANSI: 4
sd 3:0:0:0: [sda] 623769600 512-byte logical blocks: (319 GB/297 GiB)
sd 3:0:0:0: [sda] Write Protect is off
sd 3:0:0:0: [sda] No Caching mode page present
sd 3:0:0:0: [sda] Assuming drive cache: write through
sd 3:0:0:0: [sda] No Caching mode page present
sd 3:0:0:0: [sda] Assuming drive cache: write through
sda:
sd 3:0:0:0: [sda] No Caching mode page present
sd 3:0:0:0: [sda] Assuming drive cache: write through
sd 3:0:0:0: [sda] Attached SCSI disk

#> cat /sys/class/scsi_disk/3\:0\:0\:0/cache_type
write through
#> echo "write back" > /sys/class/scsi_disk/3\:0\:0\:0/cache_type
#>
#> echo "write back" > /sys/class/scsi_disk/3\:0\:0\:0/cache_type
#>
#>
#> cat /sys/class/scsi_disk/3\:0\:0\:0/cache_type
write through

Regards,
Amit Sahrawat

On Thu, Oct 6, 2011 at 1:38 AM, James Bottomley
<James.Bottomley-JuX6DAaQMKPCXq6kfMZ53/egYHeGw8Jk@public.gmane.org> wrote:
> On Thu, 2011-10-06 at 01:21 +0530, Amit Sahrawat wrote:
>> > The best we could probably offer is an interface to turn on the WCE bit
>> > in software (technically, you can do this today
>> > in /scsi/class/scsi_disk/<disk>/cache_type, it's just that it will try
>> > to commit the change as a MODE_SELECT which will presumably fail).
>> Thanks James, is this related with SCSI command MODE_SELECT? and this
>> is to be passed when there is some failure?
>> or simply doing an "echo <value>" to
>> /scsi/class/scsi_disk/<disk>/cache_type? can you please elaborate a
>> little
>
> You tell me since you have the device.  What that echo does is that it
> does try to make the change permanent with a mode select ... that likely
> won't work and the cache change only takes if the revalidated disk says
> the write back has been enabled (which I really think it won't).  So I
> think you need an additional software bit to flip for the case where the
> device lies.
>
> James
>
>
>
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