NTFS And 4K Disks

Since the 1960’s, hard disks have always used a block size of 512 bytes for the default read/write block size.  Recently drive manufacturers have been moving toward a larger block size to improve performance and reliability.  Currently there are two types of disks available with a 4KB sector size: 512 byte emulated, and 4KB block…

5

How Queue Deadlocks Happen

I recently worked on an interesting system hang issue with a deadlocked work queue and wanted to share some information about how we resolved the issue.   In this example, we will demonstrate how a cascaded work item can deadlock a work queue.  As you can see from the illustration, we have three worker threads. …

3

Ntfs Misreporting Free Space (Part 2)

Continuing our discussion on the internals of disk usage, we will now shift our focus to internal metadata usage. …….. KB in …. Indexes.   Consider for a moment a world without indexes…  The $MFT is a database containing records that are accessed via FRS (file record segment) numbers.  This FRS number includes an embedded sequence number…

4

NTFS Misreports Free Space?

I have recently seen a number of issues where customers called in to report a significant difference between the “Size on disk” for the root of a volume, and the reported amount of “Used space” in the volume properties.  While considering this, I noticed that my own C: drive had a mysterious 20GB difference.   Below…

14

NTDebugging Puzzler 0x00000007: Interlocked functions

  Today, we will have some fun with interlocked functions.   The following section of code is reentrant.  A “well meaning” developer used interlocked functions to avoid serializing on a global table lock.   Initial smoke testing shows that the code works fine.  Sometimes things are not as they appear when doing initial code review. …

19

Understanding NTFS Compression

As our group’s file systems expert, I see most of the common problems associated with the use/misuse of NTFS compression.  Before you check the “Compress contents to save disk space” checkbox, it might be good to understand how this affects the happy little bits, bytes, & nibbles running around on the disk. Often backup applications…

5