Hello. I have been testing the performance of XFS with "Flag Unwritten Extents" enabled and disabled. For security reasons I know XFS flags all unwritten extents by default, so that uninitialized disk space cannot be read by the user. In my application I actually want to have access to this uninitialized disk space. I have been modifying the superblocks using xfs_repair to enable this functionality. Interestingly, I have found that creating a 10 GB file using fallocate is significantly slower with unwritten flag extents disabled. For instance, creating a 10GB file takes 32 seconds on my (slow) machine, whereas with the flag enabled, the process is almost instantaneous. Does anyone know why creating an uninitialized file is so much slower when the unwritten extents flag functionality is disabled? I know that the disk is not being initialized to zero, as I can read back non zero content. For my application I'm interested in creating large uninitialised files quickly, so I'm very interested to know what additional operations are being performed with the flagging disabled. Thanks for the help. Bill. -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
