.sp
.ne 2
.na
-\fBmetaslab_debug\fR (int)
+\fBmetaslab_aliquot\fR (ulong)
.ad
.RS 12n
-Keep space maps in core to verify frees
+Metaslab granularity, in bytes. This is roughly similar to what would be
+referred to as the "stripe size" in traditional RAID arrays. In normal
+operation, ZFS will try to write this amount of data to a top-level vdev
+before moving on to the next one.
+.sp
+Default value: \fB524,288\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBmetaslab_bias_enabled\fR (int)
+.ad
+.RS 12n
+Enable metaslab group biasing based on its vdev's over- or under-utilization
+relative to the pool.
+.sp
+Use \fB1\fR for yes (default) and \fB0\fR for no.
+.RE
+
+.sp
+.ne 2
+.na
+\fBmetaslab_debug_load\fR (int)
+.ad
+.RS 12n
+Load all metaslabs during pool import.
.sp
Use \fB1\fR for yes and \fB0\fR for no (default).
.RE
+.sp
+.ne 2
+.na
+\fBmetaslab_debug_unload\fR (int)
+.ad
+.RS 12n
+Prevent metaslabs from being unloaded.
+.sp
+Use \fB1\fR for yes and \fB0\fR for no (default).
+.RE
+
+.sp
+.ne 2
+.na
+\fBmetaslab_fragmentation_factor_enabled\fR (int)
+.ad
+.RS 12n
+Enable use of the fragmentation metric in computing metaslab weights.
+.sp
+Use \fB1\fR for yes (default) and \fB0\fR for no.
+.RE
+
+.sp
+.ne 2
+.na
+\fBmetaslabs_per_vdev\fR (int)
+.ad
+.RS 12n
+When a vdev is added, it will be divided into approximately (but no more than) this number of metaslabs.
+.sp
+Default value: \fB200\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBmetaslab_preload_enabled\fR (int)
+.ad
+.RS 12n
+Enable metaslab group preloading.
+.sp
+Use \fB1\fR for yes (default) and \fB0\fR for no.
+.RE
+
+.sp
+.ne 2
+.na
+\fBmetaslab_lba_weighting_enabled\fR (int)
+.ad
+.RS 12n
+Give more weight to metaslabs with lower LBAs, assuming they have
+greater bandwidth as is typically the case on a modern constant
+angular velocity disk drive.
+.sp
+Use \fB1\fR for yes (default) and \fB0\fR for no.
+.RE
+
.sp
.ne 2
.na
Default value: 24
.RE
+.sp
+.ne 2
+.na
+\fBspa_load_verify_data\fR (int)
+.ad
+.RS 12n
+Whether to traverse data blocks during an "extreme rewind" (\fB-X\fR)
+import. Use 0 to disable and 1 to enable.
+
+An extreme rewind import normally performs a full traversal of all
+blocks in the pool for verification. If this parameter is set to 0,
+the traversal skips non-metadata blocks. It can be toggled once the
+import has started to stop or start the traversal of non-metadata blocks.
+.sp
+Default value: 1
+.RE
+
+.sp
+.ne 2
+.na
+\fBspa_load_verify_metadata\fR (int)
+.ad
+.RS 12n
+Whether to traverse blocks during an "extreme rewind" (\fB-X\fR)
+pool import. Use 0 to disable and 1 to enable.
+
+An extreme rewind import normally performs a full traversal of all
+blocks in the pool for verification. If this parameter is set to 1,
+the traversal is not performed. It can be toggled once the import has
+started to stop or start the traversal.
+.sp
+Default value: 1
+.RE
+
+.sp
+.ne 2
+.na
+\fBspa_load_verify_maxinflight\fR (int)
+.ad
+.RS 12n
+Maximum concurrent I/Os during the traversal performed during an "extreme
+rewind" (\fB-X\fR) pool import.
+.sp
+Default value: 10000
+.RE
+
+.sp
+.ne 2
+.na
+\fBspa_slop_shift\fR (int)
+.ad
+.RS 12n
+Normally, we don't allow the last 3.2% (1/(2^spa_slop_shift)) of space
+in the pool to be consumed. This ensures that we don't run the pool
+completely out of space, due to unaccounted changes (e.g. to the MOS).
+It also limits the worst-case time to allocate space. If we have
+less than this amount of free space, most ZPL operations (e.g. write,
+create) will return ENOSPC.
+.sp
+Default value: 5
+.RE
+
.sp
.ne 2
.na
\fBzfetch_array_rd_sz\fR (ulong)
.ad
.RS 12n
-Number of bytes in a array_read
+If prefetching is enabled, disable prefetching for reads larger than this size.
.sp
Default value: \fB1,048,576\fR.
.RE
\fBzfetch_block_cap\fR (uint)
.ad
.RS 12n
-Max number of blocks to fetch at a time
+Max number of blocks to prefetch at a time
.sp
Default value: \fB256\fR.
.RE
\fBzfetch_max_streams\fR (uint)
.ad
.RS 12n
-Max number of streams per zfetch
+Max number of streams per zfetch (prefetch streams per file).
.sp
Default value: \fB8\fR.
.RE
\fBzfetch_min_sec_reap\fR (uint)
.ad
.RS 12n
-Min time before stream reclaim
+Min time before an active prefetch stream can be reclaimed
.sp
Default value: \fB2\fR.
.RE
+.sp
+.ne 2
+.na
+\fBzfs_arc_average_blocksize\fR (int)
+.ad
+.RS 12n
+The ARC's buffer hash table is sized based on the assumption of an average
+block size of \fBzfs_arc_average_blocksize\fR (default 8K). This works out
+to roughly 1MB of hash table per 1GB of physical memory with 8-byte pointers.
+For configurations with a known larger average block size this value can be
+increased to reduce the memory footprint.
+
+.sp
+Default value: \fB8192\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_arc_evict_batch_limit\fR (int)
+.ad
+.RS 12n
+Number ARC headers to evict per sub-list before proceeding to another sub-list.
+This batch-style operation prevents entire sub-lists from being evicted at once
+but comes at a cost of additional unlocking and locking.
+.sp
+Default value: \fB10\fR.
+.RE
+
.sp
.ne 2
.na
Default value: \fB5\fR.
.RE
+.sp
+.ne 2
+.na
+\fBzfs_arc_lotsfree_percent\fR (int)
+.ad
+.RS 12n
+Throttle I/O when free system memory drops below this percentage of total
+system memory. Setting this value to 0 will disable the throttle.
+.sp
+Default value: \fB10\fR.
+.RE
+
.sp
.ne 2
.na
.sp
.ne 2
.na
-\fBzfs_arc_memory_throttle_disable\fR (int)
+\fBzfs_arc_meta_limit\fR (ulong)
.ad
.RS 12n
-Disable memory throttle
+The maximum allowed size in bytes that meta data buffers are allowed to
+consume in the ARC. When this limit is reached meta data buffers will
+be reclaimed even if the overall arc_c_max has not been reached. This
+value defaults to 0 which indicates that 3/4 of the ARC may be used
+for meta data.
.sp
-Use \fB1\fR for yes (default) and \fB0\fR to disable.
+Default value: \fB0\fR.
.RE
.sp
.ne 2
.na
-\fBzfs_arc_meta_limit\fR (ulong)
+\fBzfs_arc_meta_min\fR (ulong)
.ad
.RS 12n
-Meta limit for arc size
+The minimum allowed size in bytes that meta data buffers may consume in
+the ARC. This value defaults to 0 which disables a floor on the amount
+of the ARC devoted meta data.
.sp
Default value: \fB0\fR.
.RE
\fBzfs_arc_meta_prune\fR (int)
.ad
.RS 12n
-Bytes of meta data to prune
+The number of dentries and inodes to be scanned looking for entries
+which can be dropped. This may be required when the ARC reaches the
+\fBzfs_arc_meta_limit\fR because dentries and inodes can pin buffers
+in the ARC. Increasing this value will cause to dentry and inode caches
+to be pruned more aggressively. Setting this value to 0 will disable
+pruning the inode and dentry caches.
.sp
-Default value: \fB1,048,576\fR.
+Default value: \fB10,000\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_arc_meta_adjust_restarts\fR (ulong)
+.ad
+.RS 12n
+The number of restart passes to make while scanning the ARC attempting
+the free buffers in order to stay below the \fBzfs_arc_meta_limit\fR.
+This value should not need to be tuned but is available to facilitate
+performance analysis.
+.sp
+Default value: \fB4096\fR.
.RE
.sp
.sp
.ne 2
.na
+\fBzfs_arc_num_sublists_per_state\fR (int)
+.ad
+.RS 12n
+To allow more fine-grained locking, each ARC state contains a series
+of lists for both data and meta data objects. Locking is performed at
+the level of these "sub-lists". This parameters controls the number of
+sub-lists per ARC state.
+.sp
+Default value: 1 or the number of on-online CPUs, whichever is greater
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_arc_overflow_shift\fR (int)
+.ad
+.RS 12n
+The ARC size is considered to be overflowing if it exceeds the current
+ARC target size (arc_c) by a threshold determined by this parameter.
+The threshold is calculated as a fraction of arc_c using the formula
+"arc_c >> \fBzfs_arc_overflow_shift\fR".
+
+The default value of 8 causes the ARC to be considered to be overflowing
+if it exceeds the target size by 1/256th (0.3%) of the target size.
+
+When the ARC is overflowing, new buffer allocations are stalled until
+the reclaim thread catches up and the overflow condition no longer exists.
+.sp
+Default value: \fB8\fR.
+.RE
+
+.sp
+.ne 2
+.na
+
\fBzfs_arc_p_min_shift\fR (int)
.ad
.RS 12n
Use \fB1\fR for yes (default) and \fB0\fR to disable.
.RE
+.sp
+.ne 2
+.na
+\fBzfs_arc_p_dampener_disable\fR (int)
+.ad
+.RS 12n
+Disable arc_p adapt dampener
+.sp
+Use \fB1\fR for yes (default) and \fB0\fR to disable.
+.RE
+
.sp
.ne 2
.na
Default value: \fB5\fR.
.RE
+.sp
+.ne 2
+.na
+\fBzfs_arc_sys_free\fR (ulong)
+.ad
+.RS 12n
+The target number of bytes the ARC should leave as free memory on the system.
+Defaults to the larger of 1/64 of physical memory or 512K. Setting this
+option to a non-zero value will override the default.
+.sp
+Default value: \fB0\fR.
+.RE
+
.sp
.ne 2
.na
\fBzfs_autoimport_disable\fR (int)
.ad
.RS 12n
-Disable pool import at module load
+Disable pool import at module load by ignoring the cache file (typically \fB/etc/zfs/zpool.cache\fR).
.sp
-Use \fB1\fR for yes and \fB0\fR for no (default).
+Use \fB1\fR for yes (default) and \fB0\fR for no.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_dbgmsg_enable\fR (int)
+.ad
+.RS 12n
+Internally ZFS keeps a small log to facilitate debugging. By default the log
+is disabled, to enable it set this option to 1. The contents of the log can
+be accessed by reading the /proc/spl/kstat/zfs/dbgmsg file. Writing 0 to
+this proc file clears the log.
+.sp
+Default value: \fB0\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_dbgmsg_maxsize\fR (int)
+.ad
+.RS 12n
+The maximum size in bytes of the internal ZFS debug log.
+.sp
+Default value: \fB4M\fR.
.RE
.sp
.RS 12n
Enable prefetching dedup-ed blks
.sp
-Use \fB1\fR for yes (default) and \fB0\fR to disable.
+Use \fB1\fR for yes and \fB0\fR to disable (default).
.RE
.sp
Default value: \fB67,108,864\fR.
.RE
+.sp
+.ne 2
+.na
+\fBzfs_free_max_blocks\fR (ulong)
+.ad
+.RS 12n
+Maximum number of blocks freed in a single txg.
+.sp
+Default value: \fB100,000\fR.
+.RE
+
.sp
.ne 2
.na
Default value: \fB300\fR.
.RE
+.sp
+.ne 2
+.na
+\fBzfs_admin_snapshot\fR (int)
+.ad
+.RS 12n
+Allow the creation, removal, or renaming of entries in the .zfs/snapshot
+directory to cause the creation, destruction, or renaming of snapshots.
+When enabled this functionality works both locally and over NFS exports
+which have the 'no_root_squash' option set. This functionality is disabled
+by default.
+.sp
+Use \fB1\fR for yes and \fB0\fR for no (default).
+.RE
+
.sp
.ne 2
.na
\fBzfs_flags\fR (int)
.ad
.RS 12n
-Set additional debugging flags
+Set additional debugging flags. The following flags may be bitwise-or'd
+together.
+.sp
+.TS
+box;
+rB lB
+lB lB
+r l.
+Value Symbolic Name
+ Description
+_
+1 ZFS_DEBUG_DPRINTF
+ Enable dprintf entries in the debug log.
+_
+2 ZFS_DEBUG_DBUF_VERIFY *
+ Enable extra dbuf verifications.
+_
+4 ZFS_DEBUG_DNODE_VERIFY *
+ Enable extra dnode verifications.
+_
+8 ZFS_DEBUG_SNAPNAMES
+ Enable snapshot name verification.
+_
+16 ZFS_DEBUG_MODIFY
+ Check for illegally modified ARC buffers.
+_
+32 ZFS_DEBUG_SPA
+ Enable spa_dbgmsg entries in the debug log.
+_
+64 ZFS_DEBUG_ZIO_FREE
+ Enable verification of block frees.
+_
+128 ZFS_DEBUG_HISTOGRAM_VERIFY
+ Enable extra spacemap histogram verifications.
+.TE
+.sp
+* Requires debug build.
.sp
-Default value: \fB1\fR.
+Default value: \fB0\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_free_leak_on_eio\fR (int)
+.ad
+.RS 12n
+If destroy encounters an EIO while reading metadata (e.g. indirect
+blocks), space referenced by the missing metadata can not be freed.
+Normally this causes the background destroy to become "stalled", as
+it is unable to make forward progress. While in this stalled state,
+all remaining space to free from the error-encountering filesystem is
+"temporarily leaked". Set this flag to cause it to ignore the EIO,
+permanently leak the space from indirect blocks that can not be read,
+and continue to free everything else that it can.
+
+The default, "stalling" behavior is useful if the storage partially
+fails (i.e. some but not all i/os fail), and then later recovers. In
+this case, we will be able to continue pool operations while it is
+partially failed, and when it recovers, we can continue to free the
+space, with no leaks. However, note that this case is actually
+fairly rare.
+
+Typically pools either (a) fail completely (but perhaps temporarily,
+e.g. a top-level vdev going offline), or (b) have localized,
+permanent errors (e.g. disk returns the wrong data due to bit flip or
+firmware bug). In case (a), this setting does not matter because the
+pool will be suspended and the sync thread will not be able to make
+forward progress regardless. In case (b), because the error is
+permanent, the best we can do is leak the minimum amount of space,
+which is what setting this flag will do. Therefore, it is reasonable
+for this flag to normally be set, but we chose the more conservative
+approach of not setting it, so that there is no possibility of
+leaking space in the "partial temporary" failure case.
+.sp
+Default value: \fB0\fR.
.RE
.sp
Default value: \fB32,768\fR.
.RE
+.sp
+.ne 2
+.na
+\fBzfs_max_recordsize\fR (int)
+.ad
+.RS 12n
+We currently support block sizes from 512 bytes to 16MB. The benefits of
+larger blocks, and thus larger IO, need to be weighed against the cost of
+COWing a giant block to modify one byte. Additionally, very large blocks
+can have an impact on i/o latency, and also potentially on the memory
+allocator. Therefore, we do not allow the recordsize to be set larger than
+zfs_max_recordsize (default 1MB). Larger blocks can be created by changing
+this tunable, and pools with larger blocks can always be imported and used,
+regardless of this setting.
+.sp
+Default value: \fB1,048,576\fR.
+.RE
+
.sp
.ne 2
.na
Use \fB1\fR for yes and \fB0\fR for no (default).
.RE
+.sp
+.ne 2
+.na
+\fBzfs_metaslab_fragmentation_threshold\fR (int)
+.ad
+.RS 12n
+Allow metaslabs to keep their active state as long as their fragmentation
+percentage is less than or equal to this value. An active metaslab that
+exceeds this threshold will no longer keep its active status allowing
+better metaslabs to be selected.
+.sp
+Default value: \fB70\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_mg_fragmentation_threshold\fR (int)
+.ad
+.RS 12n
+Metaslab groups are considered eligible for allocations if their
+fragmenation metric (measured as a percentage) is less than or equal to
+this value. If a metaslab group exceeds this threshold then it will be
+skipped unless all metaslab groups within the metaslab class have also
+crossed this threshold.
+.sp
+Default value: \fB85\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_mg_noalloc_threshold\fR (int)
+.ad
+.RS 12n
+Defines a threshold at which metaslab groups should be eligible for
+allocations. The value is expressed as a percentage of free space
+beyond which a metaslab group is always eligible for allocations.
+If a metaslab group's free space is less than or equal to the
+threshold, the allocator will avoid allocating to that group
+unless all groups in the pool have reached the threshold. Once all
+groups have reached the threshold, all groups are allowed to accept
+allocations. The default value of 0 disables the feature and causes
+all metaslab groups to be eligible for allocations.
+
+This parameter allows to deal with pools having heavily imbalanced
+vdevs such as would be the case when a new vdev has been added.
+Setting the threshold to a non-zero percentage will stop allocations
+from being made to vdevs that aren't filled to the specified percentage
+and allow lesser filled vdevs to acquire more allocations than they
+otherwise would under the old \fBzfs_mg_alloc_failures\fR facility.
+.sp
+Default value: \fB0\fR.
+.RE
+
.sp
.ne 2
.na
.sp
.ne 2
.na
-\fBzfs_pd_blks_max\fR (int)
+\fBzfs_pd_bytes_max\fR (int)
.ad
.RS 12n
-Max number of blocks to prefetch
+The number of bytes which should be prefetched.
.sp
-Default value: \fB100\fR.
+Default value: \fB52,428,800\fR.
.RE
.sp
\fBzfs_resilver_delay\fR (int)
.ad
.RS 12n
-Number of ticks to delay resilver
+Number of ticks to delay prior to issuing a resilver I/O operation when
+a non-resilver or non-scrub I/O operation has occurred within the past
+\fBzfs_scan_idle\fR ticks.
.sp
Default value: \fB2\fR.
.RE
\fBzfs_scan_idle\fR (int)
.ad
.RS 12n
-Idle window in clock ticks
+Idle window in clock ticks. During a scrub or a resilver, if
+a non-scrub or non-resilver I/O operation has occurred during this
+window, the next scrub or resilver operation is delayed by, respectively
+\fBzfs_scrub_delay\fR or \fBzfs_resilver_delay\fR ticks.
.sp
Default value: \fB50\fR.
.RE
\fBzfs_scrub_delay\fR (int)
.ad
.RS 12n
-Number of ticks to delay scrub
+Number of ticks to delay prior to issuing a scrub I/O operation when
+a non-scrub or non-resilver I/O operation has occurred within the past
+\fBzfs_scan_idle\fR ticks.
.sp
Default value: \fB4\fR.
.RE
\fBzfs_top_maxinflight\fR (int)
.ad
.RS 12n
-Max I/Os per top-level
+Max I/Os per top-level vdev during scrub or resilver operations.
.sp
Default value: \fB32\fR.
.RE
Default value: \fB1,048,576\fR.
.RE
-.sp
-.ne 2
-.na
-\fBzio_bulk_flags\fR (int)
-.ad
-.RS 12n
-Additional flags to pass to bulk buffers
-.sp
-Default value: \fB0\fR.
-.RE
-
.sp
.ne 2
.na
\fBzio_delay_max\fR (int)
.ad
.RS 12n
-Max zio millisec delay before posting event
+Max zio millisecond delay before posting event
.sp
Default value: \fB30,000\fR.
.RE
.sp
.ne 2
.na
-\fBzio_injection_enabled\fR (int)
+\fBzio_requeue_io_start_cut_in_line\fR (int)
.ad
.RS 12n
-Enable fault injection
+Prioritize requeued I/O
.sp
-Use \fB1\fR for yes and \fB0\fR for no (default).
+Default value: \fB0\fR.
.RE
.sp
.ne 2
.na
-\fBzio_requeue_io_start_cut_in_line\fR (int)
+\fBzio_taskq_batch_pct\fR (uint)
.ad
.RS 12n
-Prioritize requeued I/O
+Percentage of online CPUs (or CPU cores, etc) which will run a worker thread
+for IO. These workers are responsible for IO work such as compression and
+checksum calculations. Fractional number of CPUs will be rounded down.
.sp
-Default value: \fB0\fR.
+The default value of 75 was chosen to avoid using all CPUs which can result in
+latency issues and inconsistent application performance, especially when high
+compression is enabled.
+.sp
+Default value: \fB75\fR.
.RE
.sp
.sp
.ne 2
.na
-\fBzvol_threads\fR (uint)
+\fBzvol_prefetch_bytes\fR (uint)
.ad
.RS 12n
-Number of threads for zvol device
+When adding a zvol to the system prefetch \fBzvol_prefetch_bytes\fR
+from the start and end of the volume. Prefetching these regions
+of the volume is desirable because they are likely to be accessed
+immediately by \fBblkid(8)\fR or by the kernel scanning for a partition
+table.
.sp
-Default value: \fB32\fR.
+Default value: \fB131,072\fR.
.RE
.SH ZFS I/O SCHEDULER
projects / mirror_zfs.git / blobdiff