RE: OOB Test fails

[Danesh Daroui <Danesh.Daroui@ascom.com>]

Hi Steve,

Thank you for your prompt answer. When I run OOB test (mtd_oobtest), for instance, one of devices always return verification failed error on a certain address. This is all we know and all the test reports. We use a quite old kernel i.e. 2.6.39 and this is one of the things that we suspect as a source of the problem that the kernel is outdated. Also, we consider the hardware failure since on some devices no error is shown on OOB test while on others more errors are shown and the address is changed randomly sometimes.

Our main problem is that sometimes UBIFS forces the device into read-only mode due to "bad CRC" error at startup when the device is booted. I am now running tests which are in "mtd_utils" for testing file system. I have started running two tests which are "simple/test_1" and "simple/test_2" which simply write until the drive is full and the read the data back and verify the correctness. During the test, I see lots of:

UBI: scrubbed PEB 585 (LEB 3:770), data moved to PEB 1772
UBI: scrubbed PEB 1045 (LEB 3:1261), data moved to PEB 828
UBI: scrubbed PEB 1493 (LEB 3:664), data moved to PEB 814
UBI: scrubbed PEB 751 (LEB 3:1260), data moved to PEB 1772

In my mind, this is related to problematic hardware that the data is corrupted on many cells that UBIFS tries to move the data when a corruption is detected. My question is, whether this guess can be valid or this is mostly due to old kernel that we are using and upgrading to a new kernel would most likely solve the problems?

Thanks again,

Danesh Daroui


-----Original Message-----
From: Steve deRosier [mailto:derosier@gmail.com] 
Sent: den 26 oktober 2016 18:17
To: Danesh Daroui <Danesh.Daroui@ascom.com>
Cc: linux-mtd@lists.infradead.org
Subject: Re: OOB Test fails

Hi Danesh,


On Wed, Oct 26, 2016 at 9:07 AM, Danesh Daroui <Danesh.Daroui@ascom.com> wrote:
> Hello all,
>
> I have executed MTD tests against an unmounted MTD device which uses UBIFS. All MTD tests except OOB test is passed where the OOB test fails from time to time and from device to device. I have read here:
>
> http://www.linux-mtd.infradead.org/faq/ubi.html#L_why_no_oob
>
> that UBIFS does not use OOB area. Therefore wanted to ask if failing this test does not need that there is any problem in our system (both HW and SW/configuration) and we can safely ignore the results for this test.
>

UBIFS doesn't use the OOB area, but your MTD driver most likely does.
We don't want UBI or UBIFS messing with the OOB area because your flash, NAND controller and the MTD driver will use that. Bad block markers are set in the OOB area by the manufacturer in most NAND flashes and your controller and MTD driver will store and use the bits in the OOB to do error correction.

So, in short - the OOB area does need to function correctly.  As to if and why the OOB test is or isn't working is a different issue and I have no input on that.  All that depends on your mix of flash, controller and driver.

- Steve