-
Notifications
You must be signed in to change notification settings - Fork 1.7k
New issue
Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.
By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.
Already on GitHub? Sign in to your account
Fix dRAID self-healing short columns #12010
Merged
Merged
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
When dRAID performs a normal read operation only the data columns in the raid map are read from disk. This is enough information to calculate the checksum, verify it, and return the needed data to the application. It's only in the event of a checksum failure that the additional parity and any empty columns must be read since they are required for parity reconstrction. Reading these additional columns is handled by vdev_raidz_read_all() which calls vdev_draid_map_alloc_empty() to expand the raid_map_t and submit IOs for the missing columns. This all works corretly, but it fails to account for any "short" columns. These are data columns which are padded with a empty skip sector at the end. Since that empty sector is not needed for a normal read it's not read when columns is first read from disk. However, like the parity and empty columns the skip sector is needed to perform reconstruction. The fix is to mark any "short" columns as never being read by clearing the rc_tried flag when expanding the raid_map_t. This will cause the entire column to re-read from disk in the event of a checksum failure allowing the self-healing functionality to repair the block. Note that this only effects the self-healing feature because when scrubbing a pool the parity, data, and empty columns are all read initially to verify their contents. Furthermore, only blocks which contain "short" columns would be effected, and only when the memory backing the skip sector wasn't already zeroed out. This change extends the existing redundancy_raidz.ksh test case to verify self-healing (as well as resilver and scrub). Then applies the same test case to dRAID with a slightly modified version of the test script called redundancy_draid.ksh. The unused variable combrec was also removed from both test cases. Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
ahrens
approved these changes
May 7, 2021
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
Thanks for the thorough explanation!
mmaybee
approved these changes
May 7, 2021
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
Nice work
behlendorf
added
Status: Accepted
Ready to integrate (reviewed, tested)
and removed
Status: Code Review Needed
Ready for review and testing
labels
May 7, 2021
behlendorf
added a commit
to behlendorf/zfs
that referenced
this pull request
May 10, 2021
When dRAID performs a normal read operation only the data columns in the raid map are read from disk. This is enough information to calculate the checksum, verify it, and return the needed data to the application. It's only in the event of a checksum failure that the additional parity and any empty columns must be read since they are required for parity reconstruction. Reading these additional columns is handled by vdev_raidz_read_all() which calls vdev_draid_map_alloc_empty() to expand the raid_map_t and submit IOs for the missing columns. This all works correctly, but it fails to account for any "short" columns. These are data columns which are padded with a empty skip sector at the end. Since that empty sector is not needed for a normal read it's not read when columns is first read from disk. However, like the parity and empty columns the skip sector is needed to perform reconstruction. The fix is to mark any "short" columns as never being read by clearing the rc_tried flag when expanding the raid_map_t. This will cause the entire column to re-read from disk in the event of a checksum failure allowing the self-healing functionality to repair the block. Note that this only effects the self-healing feature because when scrubbing a pool the parity, data, and empty columns are all read initially to verify their contents. Furthermore, only blocks which contain "short" columns would be effected, and only when the memory backing the skip sector wasn't already zeroed out. This change extends the existing redundancy_raidz.ksh test case to verify self-healing (as well as resilver and scrub). Then applies the same test case to dRAID with a slightly modified version of the test script called redundancy_draid.ksh. The unused variable combrec was also removed from both test cases. Reviewed-by: Matthew Ahrens <mahrens@delphix.com> Reviewed-by: Mark Maybee <mark.maybee@delphix.com> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes openzfs#12010
sempervictus
pushed a commit
to sempervictus/zfs
that referenced
this pull request
May 31, 2021
When dRAID performs a normal read operation only the data columns in the raid map are read from disk. This is enough information to calculate the checksum, verify it, and return the needed data to the application. It's only in the event of a checksum failure that the additional parity and any empty columns must be read since they are required for parity reconstruction. Reading these additional columns is handled by vdev_raidz_read_all() which calls vdev_draid_map_alloc_empty() to expand the raid_map_t and submit IOs for the missing columns. This all works correctly, but it fails to account for any "short" columns. These are data columns which are padded with a empty skip sector at the end. Since that empty sector is not needed for a normal read it's not read when columns is first read from disk. However, like the parity and empty columns the skip sector is needed to perform reconstruction. The fix is to mark any "short" columns as never being read by clearing the rc_tried flag when expanding the raid_map_t. This will cause the entire column to re-read from disk in the event of a checksum failure allowing the self-healing functionality to repair the block. Note that this only effects the self-healing feature because when scrubbing a pool the parity, data, and empty columns are all read initially to verify their contents. Furthermore, only blocks which contain "short" columns would be effected, and only when the memory backing the skip sector wasn't already zeroed out. This change extends the existing redundancy_raidz.ksh test case to verify self-healing (as well as resilver and scrub). Then applies the same test case to dRAID with a slightly modified version of the test script called redundancy_draid.ksh. The unused variable combrec was also removed from both test cases. Reviewed-by: Matthew Ahrens <mahrens@delphix.com> Reviewed-by: Mark Maybee <mark.maybee@delphix.com> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes openzfs#12010
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Motivation and Context
When stress testing dRAID it was observed that there were some blocks
that could not be self-healed yet could be repaired by a pool scrub.
This was unexpected since anything which can be repaired by a scrub
must also be able to self-heal.
Description
When dRAID performs a normal read operation only the data columns
in the raid map are read from disk. This is enough information to
calculate the checksum, verify it, and return the needed data to the
application. It's only in the event of a checksum failure that the
additional parity and any empty columns must be read since they are
required for parity reconstruction.
Reading these additional columns is handled by vdev_raidz_read_all()
which calls vdev_draid_map_alloc_empty() to expand the raid_map_t
and submit IOs for the missing columns. This all works correctly,
but it fails to account for any "short" columns. These are data
columns which are padded with a empty skip sector at the end.
Since that empty sector is not needed for a normal read it's not
read when the column is first read from disk. However, like the parity
and empty columns the skip sector is needed to perform reconstruction.
The fix is to mark any "short" columns as never being read by clearing
the rc_tried flag when expanding the raid_map_t. This will cause
the entire column to re-read from disk in the event of a checksum
failure allowing the self-healing functionality to repair the block.
Note that this only effects the self-healing feature because when
scrubbing a pool the full parity, data, and empty columns are read
initially to verify their contents. Furthermore, only blocks which
contain "short" columns would be effected, and only when the memory
backing the skip sector wasn't already zeroed out.
This change extends the existing redundancy_raidz.ksh test case to
verify self-healing (as well as resilver and scrub). Then applies
the same test case to dRAID with a slightly modified version of
the test script called redundancy_draid.ksh. The unused variable
combrec was also removed from both test cases.
How Has This Been Tested?
Added a new
redundancy_draid.ksh
test which is based on theexisting
redundancy_raidz.ksh
. Prior to this change the new testwould reliably fail, and with it applied no failures have been observed
for 100 test runs.
Types of changes
Checklist:
Signed-off-by
.