[storage] Update fragmentation metrics comments
Change-Id: I2a8b31a888d38486cd9d384ed45e8b4b2dff42c2
Reviewed-on: https://fuchsia-review.googlesource.com/c/cobalt-registry/+/684546
Reviewed-by: Steve Fung <stevefung@google.com>
Privacy-Approval: Steve Fung <stevefung@google.com>
Commit-Queue: Brandon Castellano <bcastell@google.com>
diff --git a/fuchsia/local_storage/metrics.yaml b/fuchsia/local_storage/metrics.yaml
index 6557122..81740ae 100644
--- a/fuchsia/local_storage/metrics.yaml
+++ b/fuchsia/local_storage/metrics.yaml
@@ -737,7 +737,7 @@
################################################################################
# Compression format
#
-# Total file sizes (in bytes) per compression format.
+# Total file sizes (in bytes) per compression format. Calculated on mount.
#
# Currently only supported by blobfs. When blobfs is starting up after boot, we
# compute the total (uncompressed) sizes of all blobs per compression format,
@@ -934,6 +934,8 @@
#####################################################################
# Total inodes
#
+# Calculated on mount.
+#
# Total number of inodes, either free or in use, in the system.
# The metrics will help us understand the size of inode table. This number in
# might also help understand other fragmentation metrics, namely file_in_use and
@@ -980,6 +982,8 @@
#####################################################################
# Files in use
#
+# Calculated on mount.
+#
# Total number of files, (or blobs in case of blobfs), in use in the system.
# This number may vary largely across builds or when the device has additional
# packages installed other than system base packages.
@@ -1025,6 +1029,8 @@
#####################################################################
# Extent containers in use
#
+# Calculated on mount.
+#
# File/blob may use one or more extents, a pointer to a set of blocks. Extent
# containers are collection of one or more extents. Large the number of extent
# containers in use indicate higher fragmentation of the storage.
@@ -1069,8 +1075,8 @@
################################################################################
# Extents per file fragmentation
#
-# A histogram, aggregated in-process and logged to Cobalt every time filesystem
-# is mounted or unmounted, of extents used by a file/blob.
+# A histogram of extents used by a file/blob calculated on mount.
+#
# The histogram presents fragmentation at file/blob level. This metric will help
# in understanding how defragmentation of certain files will help either to
# recover extents or to improve read performance.
@@ -1121,9 +1127,9 @@
################################################################################
# In use block fragmentation
#
-# A histogram, aggregated in-process and logged to Cobalt every time filesystem
-# is mounted or unmounted, of used contiguous blocks that represent contiguous
-# offset of a file.
+# A histogram of used contiguous blocks (representing contiguous offsets of a
+# file) calculated on mount.
+#
# The histogram shows used block fragmentation. This metric will help
# in understand the effects of block allocation policy. The metric will also
# help in targeting what blocks to move if we decide to defragment the system.
@@ -1174,8 +1180,8 @@
################################################################################
# Free fragments.
#
-# A histogram, aggregated in-process and logged to Cobalt every time filesystem
-# is mounted or unmounted, of contiguous free blocks.
+# A histogram of contiguous free blocks calculated on each mount.
+#
# The histogram shows free block fragmentation. This metric will help
# in understand likelyhood of running out of extents during a OTA.
################################################################################
