From linux-btrfs Fri Aug 06 11:30:39 2010 From: Sami Liedes Date: Fri, 06 Aug 2010 11:30:39 +0000 To: linux-btrfs Subject: Re: Number of hard links limit Message-Id: <20100806113039.GA18858 () lh ! kyla ! fi> X-MARC-Message: https://marc.info/?l=linux-btrfs&m=128109425007726 MIME-Version: 1 Content-Type: multipart/mixed; boundary="--J2SCkAp4GZ/dPZZf" --J2SCkAp4GZ/dPZZf Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Tue, Aug 03, 2010 at 12:22:14AM +0200, Oystein Viggen wrote: > IIRC, the limit on hard links is per directory. That is, if you put > each hard link into its own directory, there's basically no limit to the > amount of hard links you can make to one file. Yes, that's always pointed out in these threads. Still, it seems to be breaking real use cases also beyond backuppc (someone mentioned installing some Gentoo package). > Thus, many generations of backup with BackupPC shouldn't trigger the > problem, as each generation is stored in its own directory tree. The > problem appears when your source data has many identical files in the > same directory, since these would be deduplicated as hard links to the > same file in the backup pool. I think you are right. I looked at the errors I reported in https://bugzilla.kernel.org/show_bug.cgi?id=15762 and figured out what happens there. In dbus's source tree, under doc/api/man/man3dbus, there are 119 files with the content ".so man3dbus/DBusProtocol.3dbus". I think these are redirects to a single man page. Interestingly (and only somewhat off-topic), because of deduplication backuppc can be used to explore the merits of deduplication in filesystems too. I looked at the files I have most copies of. Many of them seem perhaps a bit silly. The most common file has a single line with the text "# dummy". I have 54991 copies of that file. They are some kind of dependency files (perhaps by libtool or something?), always in a directory named .deps and with a file extension of .Po or .Plo. There are also tens of thousands of copies of a file with a single line with the text "END". Subversion VCS seems to have two of these for every file under version control. In fact a large portion of the most common files seem to be owned by Subversion. Sami --J2SCkAp4GZ/dPZZf Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux) iQIcBAEBCAAGBQJMW/JeAAoJEKLT589SE0a06BsQAIFI+ik1aU30Ug8hYTAWvBdc 5QsCl70OLDToZcu0PVmX4V+TdPHo+XcoSVtDjb+Hxatm/AOPr8SpsFFP0gJALV+A 7Ri6INdB4503vR3nZnSAfhylY/m9xL2eq651Kx/FoPnOVbf3lTAgnCLxXtMGiF17 Y38MmoLQ3yEe5Q/DYz7ZRZYwr29DwkalREIGbIpaiKYBTh0bb57uMlwW2UO0N5/A 0cYeu3JVEgdLRh6TOxBlK+R1UAzV341cs2ct8Jcbg2SyGsY2nLFtEyShggJyiazU xEFkS6avbe/O1qOpd8ZQkM6J2Rf9LV5oCrRCEqU4gJP0QJzEghxF47jtgKvFpqm5 0SWpFke+7g9BFwZwVj4d4kfBhosFaWeAdWRdP6oDHB7YaBkLhM+U2Dc6dVPdo/Ye oPPwjv/0u6GtPOyUJbDUvPVHgIMDBk5cxAnl9LEXOzi4SUf9VzcgiTdfUdYma8iE hyv3zsJTRUeBQvV3D2Y0soyf3fzogt2cGiPb8+g9FaEqgHimGFO06clcjRt/bwyB nqK075O1lPVa623CiXUXIiPTLaffMcbLwvEpBS9tjCrBcYqT6at5fOFlONOpocnZ vHQy5R8Idf3065rxjyrlaNjpelRaFQMVPXEXUWbR+FHqaUbnWnuW7FQQBecgHESq gjOczs8GGJqZDcWANi/M =mLLb -----END PGP SIGNATURE----- --J2SCkAp4GZ/dPZZf-- -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html