Taed,
Thank you for reporting this. I have filed a bug against CHKDSK to have this investigated. If we can verify this problem still exists we will fix this by reducing the size of the requests we make to the storage system.
Neal Christiansen
Microsoft File System Filter Group Lead
This posting is provided “AS IS” with no warranties, and confers no rights
From: xxxxx@lists.osr.com [mailto:xxxxx@lists.osr.com] On Behalf Of Taed Wynnell
Sent: Tuesday, December 21, 2004 5:27 PM
To: Windows File Systems Devs Interest List
Subject: [ntfsd] Surprising bug in WinNT (and others?) CHKDSK /R bad sector checking!
Basically, the symptom was that whenever I did a CHKDSK /R on my IDE drives, it would find a huge number of bad sectors – even on brand new drives.? On a blank formatted drive, it would find around 95% bad sectors, thus rendering the drive useless.? It would do this on all of my WinNT systems.
I eventually tracked down the problem, but it’s actually an architectural issue, and I’m shocked that this bug wasn’t found previously since it’s been so many years since WinNT came out!? Plus, for all I know, this bug might exist in Windows 2000+, but the source for ATAPI.sys doesn’t seem to exist in the DDK anymore.? :-(? If anyone is able to check that out, I’d be very interested in the answer, and if yes, I’d pursue it with Microsoft (we have a Premier account).
When CHKDSK /R is searching for bad sectors in free space, it writes its pattern to a group of sectors, and then it sends down an IOCTL_DISK_VERIFY to do verification.? It tries to do this in chunks of 512 sectors (though it is usually less on non-blank drives, depending how the used sectors are interspaced with free sectors).? Class.sys gets the request and passes it off to Disk.sys, which then passes it to ScsiPort.sys as SCSIOP_VERIFY.? Finally, it ends up in ATAPI.sys as a request for the verification of 512 sectors.? As you may know, the ATA Read Verify Sectors (0x40) command can only handle 255 (actually 256 if you write a 0x00) sectors at a time since the Sector Count register is only 8 bits.
The key to this problem, though, is the discovery that on my systems, I was running the latest version of ATAPI.sys (4.0.1381.7247), which is available in a non-public KB article 832002.? With this version of the driver, the routine IdeVerify has a check that if it’s ever asked to verify more than 255 sectors, it will return the error SRB_STATUS_INVALID_REQUEST.? Unfortunately, the upper layers (not sure which) interpret that to mean that ALL of the 512 sectors that it requested must be bad sectors, and it then marks them as bad.? Arg!
So, at first it seems that they just introduced a bug.? So, I went back to the previous version of ATAPI.sys, version 4.0.1381.7210 from KB article 812780.? In there, IdeVerify also has a check if the number of sectors is greater than 255, but in that driver (and in all the previous ATAPI.sys’s that I looked at, including the DDK source), it just cuts off the sector count at 255 sectors!? It makes no attempt to inform the requestor of the lesser verification, nor does it break it up into separate I/O requests.? Thus, even though CHKDSK requested that 512 sectors be verified, it’s really only verifying 255 sectors, and then returning the status for that.? The end being when you do a CHKDSK /R, it’s really only looking for bad sectors for 49.8% of your drive.? Arg!
And I also grabbed the newest versions of chkdsk.exe, disk.sys, ntfs.sys, ftdisk.sys, class.sys, and scsiport.sys, but adding those made no difference – ATAPI.sys still receives the requests to verify 512 sectors at a time.
Unfortunately, I need a solution for this issue, but also need the functionality that the new driver gives.? And since WinNT development and bug fixing is all-but-dead at Microsoft, I’m stuck patching the new ATAPI.sys to have it only do 255 sectors whenever it requests any more than that, which limits the functionality of CHKDSK /R.? (By the way, does anyone know how to determine the new checksum for the .sys file after hand-editing it?)
But as to where the bug actually is, it’s hard to say since it’s an architectural issue – either CHKDSK needs to limit how much it checks at a time to only 255 sectors, or one of the drivers in the chain needs to break apart that request into multiple requests.
Well, I just needed to get that off my chest…? However, any comments or other suggestions would be welcomed (particularly regarding its existence in Windows 2000+)…
(Thanks for listening!)
Questions? First check the IFS FAQ at https://www.osronline.com/article.cfm?id=17
You are currently subscribed to ntfsd as: unknown lmsubst tag argument: ‘’
To unsubscribe send a blank email to xxxxx@lists.osr.com