ZFS does zfs send file system metadata flags as part of bio structure to disk drivers

L

Leo Prasath

I want to know if FreeBSD / ZFS or UFS send a flag to lower level drivers regarding File System metadata in fashion similar to Linux where the ext3/4, jfs and other file systems use the
REQ_RW_META and BIO_RW_META flags in struct request and struct bio structures respectively to tell lower level block device driver about metadata I/O.

I really appreciate any help regarding this.
 
You need to clarify what those flags do on Linux. I would though guess no because the streams created deal only with dataset contents and replicating them on receiving side requires no special actions on the underlying providers.
 
this flag is set on those block I/O requests that the file system issues to file system metadata information like inodes, journal , block allocation bitmaps etc on the disk.

E.g. this thread here : http://lists.linuxfoundation.org/pipermail/containers/2009-April/017126.html says ext3 file system sets this flag on metadata i/o requests so that it is prioritized over data i/o requests in the I/O controller for the disk.

This thread tells how ext4 tags all journal i/o with the metadata flag : http://www.spinics.net/lists/linux-ext4/msg18213.html

This thread says XFS file system tags metadata I/O requests for better merging: http://oss.sgi.com/pipermail/xfs/2009-November/004631.html
 
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