It's an artifact of metadata compression with lzjb. When you get a run of zeroes, it compresses down into the FC42 pattern. (We can clearly do better, BTW -- working on it.)
Jeff On Sat, Dec 08, 2007 at 02:18:14PM -0800, Brian Hickmann wrote: > Hello All, > > For a Operating Systems project my partner and I are investigating ZFS' on > disk layout for files and how it maintains full-stripe writes for RAIDZ. > During our investigation, we have noticed that the hex pattern 0xFC42 is > being written all over the disk and in large chunks. It seems to be written > when files are accessed or even during idle periods. It also appears both in > regular ZFS mirros as well as RAIDZ pools. The writes of this pattern are > not contained any one area of the disk either. We have tried to think of > what kind of data would be written in this manner and have come up blank. > > We thought this pattern may be related to checksums and so we tried removing > all the 20,000 or so FC42 patterns from a disk (we are using file backing > stores). We then scrubbed the pool and we got only 28 checksum errors. When > we again looked at the backing store, only about a quarter of the FC42 > pattern returned. > > Does anyone recognize this pattern and explain why this is being written to > the disk? > > Thanks, > Brian and Kynan > -- > This messages posted from opensolaris.org > _______________________________________________ > zfs-code mailing list > zfs-code at opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-code
