path: root/man
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authorAlexander Motin <mav@FreeBSD.org>2018-07-30 22:56:24 +0000
committerAlexander Motin <mav@FreeBSD.org>2018-07-30 22:56:24 +0000
commitaf8040b47abe8068cc655c0ef5f1292165dcc6d0 (patch)
tree6c0cd427a1fc1a3478fd87bbd390c84a73561cc4 /man
parent6f4662e46596a73523f38a4ea58ce348111642eb (diff)
9238 ZFS Spacemap Encoding V2
The current space map encoding has the following disadvantages: [1] Assuming 512 sector size each entry can represent at most 16MB for a segment. This makes the encoding very inefficient for large regions of space. [2] As vdev-wide space maps have started to be used by new features (i.e. device removal, zpool checkpoint) we've started imposing limits in the vdevs that can be used with them based on the maximum addressable offset (currently 64PB for a top-level vdev). The new remains backwards compatible with the old one. The introduced two-word entry format, besides extending the limits imposed by the single-entry layout, also includes a vdev field and some extra padding after its prefix. The extra padding after the prefix should is reserved for future usage (e.g. new prefixes for future encodings or new fields for flags). The new vdev field not only makes the space maps more self-descriptive, but also opens the doors for pool-wide space maps. One final important note is that the number of bits used for vdevs is reduced to 24 bits for blkptrs. That was decided as we don't know of any setups that use more than 16M vdevs for the time being and we wanted to fit the vdev field in the space map. In addition that gives us some extra bits in dva_t. illumos/illumos-gate@17f11284b49b98353b5119463254074fd9bc0a28 Reviewed by: Matt Ahrens <mahrens@delphix.com> Reviewed by: George Wilson <gwilson@zfsmail.com> Approved by: Gordon Ross <gwr@nexenta.com> Author: Serapheim Dimitropoulos <serapheim@delphix.com>
Notes: svn path=/vendor-sys/illumos/dist/; revision=336946
Diffstat (limited to 'man')
1 files changed, 28 insertions, 1 deletions
diff --git a/man/man5/zpool-features.5 b/man/man5/zpool-features.5
index b471de9cea40..f7a43e9f13f0 100644
--- a/man/man5/zpool-features.5
+++ b/man/man5/zpool-features.5
@@ -423,7 +423,6 @@ This feature becomes \fBactive\fR as soon as it is enabled and will
never return to being \fBenabled\fR.
.ne 2
@@ -488,6 +487,34 @@ This feature becomes \fBactive\fR when the "zpool checkpoint" command
is used to checkpoint the pool.
The feature will only return back to being \fBenabled\fR when the pool
is rewound or the checkpoint has been discarded.
+.ne 2
+.RS 4n
+l l .
+GUID com.delphix:spacemap_v2
+This feature enables the use of the new space map encoding which
+consists of two words (instead of one) whenever it is advantageous.
+The new encoding allows space maps to represent large regions of
+space more efficiently on-disk while also increasing their maximum
+addressable offset.
+This feature becomes \fBactive\fR once it is \fBenabled\fR, and never
+returns back to being \fBenabled\fR.
+.ne 2
.RS 4n