> Besides this, I'm still wondering about the changes in data security that > turning a database to "NoCow" would bring, i.e. would the data still be well > protected in case of a system crash or power failure ? > > I have precious data in there and wouldn't like to jeopardize its security for > a performance gain...
Quoting from the mount options of the wiki: nodatacow Do not copy-on-write data for newly created files, existing files are unaffected. This also turns off checksumming! IOW, nodatacow implies nodatasum. datacow is used to ensure the user either has access to the old version of a file, or to the newer version of the file. datacow makes sure we never have partially updated files written to disk. nodatacow gives slight performance boost by directly overwriting data (like ext[234]), at the expense of potentially getting partially updated files on system failures. Performance gain is usually < 5% unless the workload is random writes to large database files, where the difference can become very large. NOTE: switches off compression ! I don't know if the above applies for "chattr +C" as well... Perhaps someone more experienced can help. In any case, if you have precious data in there then, COW or NOCOW, you should regularly do backups to a separate, discrete filesystem. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
