Chapter 2. Introduction to Data ONTAP 45
200 difference in NVRAM usage, is an extreme case, but even for a simple 8 KB write,
caching disk blocks will consume 8 KB for the data, 8 KB for the inode update, and for large
files another 8 KB for the indirect block. WAFL logs just the 8 KB of data along with about 120
bytes of header information. With a typical mix of NFS operations, WAFL can store more than
1000 operations per megabyte of NVRAM.
Using NVRAM as a cache of unwritten disk blocks turns it into an integral part of the disk
subsystem. A failure in traditional NVRAM can corrupt the file system in ways that
fsck (a
UNIX file system repair utility) cannot detect or repair. If something goes wrong with WAFL's
NVRAM, WAFL may lose a fe