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vitastor/docs/config/osd.en.md

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Documentation → Configuration → Runtime OSD Parameters

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Runtime OSD Parameters

These parameters only apply to OSDs, are not fixed at the moment of OSD drive initialization and can be changed - either with an OSD restart or, for some of them, even without restarting by updating configuration in etcd.

etcd_report_interval

  • Type: seconds
  • Default: 5

Interval at which OSDs report their liveness to etcd. Affects OSD lease time and thus the failover speed. Lease time is equal to this parameter value plus max_etcd_attempts * etcd_quick_timeout because it should be guaranteed that every OSD always refreshes its lease in time.

etcd_stats_interval

  • Type: seconds
  • Default: 30

Interval at which OSDs report their statistics to etcd. Highly affects the imposed load on etcd, because statistics include a key for every OSD and for every PG. At the same time, low statistic intervals make vitastor-cli statistics more responsive.

run_primary

  • Type: boolean
  • Default: true

Start primary OSD logic on this OSD. As of now, can be turned off only for debugging purposes. It's possible to implement additional feature for the monitor which may allow to separate primary and secondary OSDs, but it's unclear why anyone could need it, so it's not implemented.

osd_network

  • Type: string or array of strings

Network mask of the network (IPv4 or IPv6) to use for OSDs. Note that although it's possible to specify multiple networks here, this does not mean that OSDs will create multiple listening sockets - they'll only pick the first matching address of an UP + RUNNING interface. Separate networks for cluster and client connections are also not implemented, but they are mostly useless anyway, so it's not a big deal.

bind_address

  • Type: string
  • Default: 0.0.0.0

Instead of the network mask, you can also set OSD listen address explicitly using this parameter. May be useful if you want to start OSDs on interfaces that are not UP + RUNNING.

bind_port

  • Type: integer

By default, OSDs pick random ports to use for incoming connections automatically. With this option you can set a specific port for a specific OSD by hand.

autosync_interval

  • Type: seconds
  • Default: 5
  • Can be changed online: yes

Time interval at which automatic fsyncs/flushes are issued by each OSD when the immediate_commit mode if disabled. fsyncs are required because without them OSDs quickly fill their journals, become unable to clear them and stall. Also this option limits the amount of recent uncommitted changes which OSDs may lose in case of a power outage in case when clients don't issue fsyncs at all.

autosync_writes

  • Type: integer
  • Default: 128
  • Can be changed online: yes

Same as autosync_interval, but sets the maximum number of uncommitted write operations before issuing an fsync operation internally.

recovery_queue_depth

  • Type: integer
  • Default: 1
  • Can be changed online: yes

Maximum recovery and rebalance operations initiated by each OSD in parallel. Note that each OSD talks to a lot of other OSDs so actual number of parallel recovery operations per each OSD is greater than just recovery_queue_depth. Increasing this parameter can speedup recovery if auto-tuning allows it or if it is disabled.

recovery_sleep_us

  • Type: microseconds
  • Default: 0
  • Can be changed online: yes

Delay for all recovery- and rebalance- related operations. If non-zero, such operations are artificially slowed down to reduce the impact on client I/O.

recovery_pg_switch

  • Type: integer
  • Default: 128
  • Can be changed online: yes

Number of recovery operations before switching to recovery of the next PG. The idea is to mix all PGs during recovery for more even space and load distribution but still benefit from recovery queue depth greater than 1. Degraded PGs are anyway scanned first.

recovery_sync_batch

  • Type: integer
  • Default: 16
  • Can be changed online: yes

Maximum number of recovery operations before issuing an additional fsync.

readonly

  • Type: boolean
  • Default: false

Read-only mode. If this is enabled, an OSD will never issue any writes to the underlying device. This may be useful for recovery purposes.

no_recovery

  • Type: boolean
  • Default: false
  • Can be changed online: yes

Disable automatic background recovery of objects. Note that it doesn't affect implicit recovery of objects happening during writes - a write is always made to a full set of at least pg_minsize OSDs.

no_rebalance

  • Type: boolean
  • Default: false
  • Can be changed online: yes

Disable background movement of data between different OSDs. Disabling it means that PGs in the has_misplaced state will be left in it indefinitely.

print_stats_interval

  • Type: seconds
  • Default: 3
  • Can be changed online: yes

Time interval at which OSDs print simple human-readable operation statistics on stdout.

slow_log_interval

  • Type: seconds
  • Default: 10
  • Can be changed online: yes

Time interval at which OSDs dump slow or stuck operations on stdout, if they're any. Also it's the time after which an operation is considered "slow".

inode_vanish_time

  • Type: seconds
  • Default: 60
  • Can be changed online: yes

Number of seconds after which a deleted inode is removed from OSD statistics.

max_write_iodepth

  • Type: integer
  • Default: 128
  • Can be changed online: yes

Parallel client write operation limit per one OSD. Operations that exceed this limit are pushed to a temporary queue instead of being executed immediately.

min_flusher_count

  • Type: integer
  • Default: 1
  • Can be changed online: yes

Flusher is a micro-thread that moves data from the journal to the data area of the device. Their number is auto-tuned between minimum and maximum. Minimum number is set by this parameter.

max_flusher_count

  • Type: integer
  • Default: 256
  • Can be changed online: yes

Maximum number of journal flushers (see above min_flusher_count).

inmemory_metadata

  • Type: boolean
  • Default: true

This parameter makes Vitastor always keep metadata area of the block device in memory. It's required for good performance because it allows to avoid additional read-modify-write cycles during metadata modifications. Metadata area size is currently roughly 224 MB per 1 TB of data. You can turn it off to reduce memory usage by this value, but it will hurt performance. This restriction is likely to be removed in the future along with the upgrade of the metadata storage scheme.

inmemory_journal

  • Type: boolean
  • Default: true

This parameter make Vitastor always keep journal area of the block device in memory. Turning it off will, again, reduce memory usage, but hurt performance because flusher coroutines will have to read data from the disk back before copying it into the main area. The memory usage benefit is typically very small because it's sufficient to have 16-32 MB journal for SSD OSDs. However, in theory it's possible that you'll want to turn it off for hybrid (HDD+SSD) OSDs with large journals on quick devices.

data_io

  • Type: string
  • Default: direct

I/O mode for data. One of "direct", "cached" or "directsync". Corresponds to O_DIRECT, O_SYNC and O_DIRECT|O_SYNC, respectively.

Choose "cached" to use Linux page cache. This may improve read performance for hot data and slower disks - HDDs and maybe SATA SSDs - but will slightly decrease write performance for fast disks because page cache is an overhead itself.

Choose "directsync" to use immediate_commit (which requires disable_data_fsync) with drives having write-back cache which can't be turned off, for example, Intel Optane. Also note that some desktop SSDs (for example, HP EX950) may ignore O_SYNC thus making disable_data_fsync unsafe even with "directsync".

meta_io

  • Type: string
  • Default: direct

I/O mode for metadata. One of "direct", "cached" or "directsync".

"cached" may improve read performance, but only under the following conditions:

  1. your drives are relatively slow (HDD, SATA SSD), and
  2. checksums are enabled, and
  3. inmemory_metadata is disabled. Under all these conditions, metadata blocks are read from disk on every read request to verify checksums and caching them may reduce this extra read load. Without (3) metadata is never read from the disk after starting, and without (2) metadata blocks are read from disk only during journal flushing.

"directsync" is the same as above.

If the same device is used for data and metadata, meta_io by default is set to the same value as data_io.

journal_io

  • Type: string
  • Default: direct

I/O mode for journal. One of "direct", "cached" or "directsync".

Here, "cached" may only improve read performance for recent writes and only if inmemory_journal is turned off.

If the same device is used for metadata and journal, journal_io by default is set to the same value as meta_io.

journal_sector_buffer_count

  • Type: integer
  • Default: 32

Maximum number of buffers that can be used for writing journal metadata blocks. The only situation when you should increase it to a larger value is when you enable journal_no_same_sector_overwrites. In this case set it to, for example, 1024.

journal_no_same_sector_overwrites

  • Type: boolean
  • Default: false

Enable this option for SSDs like Intel D3-S4510 and D3-S4610 which REALLY don't like when a program overwrites the same sector multiple times in a row and slow down significantly (from 25000+ iops to ~3000 iops). When this option is set, Vitastor will always move to the next sector of the journal after writing it instead of possibly overwriting it the second time.

Most (99%) other SSDs don't need this option.

throttle_small_writes

  • Type: boolean
  • Default: false
  • Can be changed online: yes

Enable soft throttling of small journaled writes. Useful for hybrid OSDs with fast journal/metadata devices and slow data devices. The idea is that small writes complete very quickly because they're first written to the journal device, but moving them to the main device is slow. So if an OSD allows clients to issue a lot of small writes it will perform very good for several seconds and then the journal will fill up and the performance will drop to almost zero. Throttling is meant to prevent this problem by artifically slowing quick writes down based on the amount of free space in the journal. When throttling is used, the performance of small writes will decrease smoothly instead of abrupt drop at the moment when the journal fills up.

throttle_target_iops

  • Type: integer
  • Default: 100
  • Can be changed online: yes

Target maximum number of throttled operations per second under the condition of full journal. Set it to approximate random write iops of your data devices (HDDs).

throttle_target_mbs

  • Type: integer
  • Default: 100
  • Can be changed online: yes

Target maximum bandwidth in MB/s of throttled operations per second under the condition of full journal. Set it to approximate linear write performance of your data devices (HDDs).

throttle_target_parallelism

  • Type: integer
  • Default: 1
  • Can be changed online: yes

Target maximum parallelism of throttled operations under the condition of full journal. Set it to approximate internal parallelism of your data devices (1 for HDDs, 4-8 for SSDs).

throttle_threshold_us

  • Type: microseconds
  • Default: 50
  • Can be changed online: yes

Minimal computed delay to be applied to throttled operations. Usually doesn't need to be changed.

osd_memlock

  • Type: boolean
  • Default: false

Lock all OSD memory to prevent it from being unloaded into swap with mlockall(). Requires sufficient ulimit -l (max locked memory).

auto_scrub

  • Type: boolean
  • Default: false
  • Can be changed online: yes

Data scrubbing is the process of background verification of copies to find and repair corrupted blocks. It's not run automatically by default since it's a new feature. Set this parameter to true to enable automatic scrubs.

This parameter makes OSDs automatically schedule data scrubbing of clean PGs every scrub_interval (see below). You can also start/schedule scrubbing manually by setting next_scrub JSON key to the desired UNIX time of the next scrub in /pg/history/... values in etcd.

no_scrub

  • Type: boolean
  • Default: false
  • Can be changed online: yes

Temporarily disable scrubbing and stop running scrubs.

scrub_interval

  • Type: string
  • Default: 30d
  • Can be changed online: yes

Default automatic scrubbing interval for all pools. Numbers without suffix are treated as seconds, possible unit suffixes include 's' (seconds), 'm' (minutes), 'h' (hours), 'd' (days), 'M' (months) and 'y' (years).

scrub_queue_depth

  • Type: integer
  • Default: 1
  • Can be changed online: yes

Number of parallel scrubbing operations per one OSD.

scrub_sleep

  • Type: milliseconds
  • Default: 0
  • Can be changed online: yes

Additional interval between two consecutive scrubbing operations on one OSD. Can be used to slow down scrubbing if it affects user load too much.

scrub_list_limit

  • Type: integer
  • Default: 1000
  • Can be changed online: yes

Number of objects to list in one listing operation during scrub.

scrub_find_best

  • Type: boolean
  • Default: true
  • Can be changed online: yes

Find and automatically restore best versions of objects with unmatched copies. In replicated setups, the best version is the version with most matching replicas. In EC setups, the best version is the subset of data and parity chunks without mismatches.

The hypothetical situation where you might want to disable it is when you have 3 replicas and you are paranoid that 2 HDDs out of 3 may silently corrupt an object in the same way (for example, zero it out) and only 1 HDD will remain good. In this case disabling scrub_find_best may help you to recover the data! See also scrub_ec_max_bruteforce below.

scrub_ec_max_bruteforce

  • Type: integer
  • Default: 100
  • Can be changed online: yes

Vitastor can locate corrupted chunks in EC setups with more than 1 parity chunk by brute-forcing all possible error locations. This configuration value limits the maximum number of checked combinations. You can try to increase it if you have EC N+K setup with N and K large enough for combination count C(N+K-1, K-1) = (N+K-1)! / (K-1)! / N! to be greater than the default 100.

If there are too many possible combinations or if multiple combinations give correct results then objects are marked inconsistent and aren't recovered automatically.

In replicated setups bruteforcing isn't needed, Vitastor just assumes that the variant with most available equal copies is correct. For example, if you have 3 replicas and 1 of them differs, this one is considered to be corrupted. But if there is no "best" version with more copies than all others have then the object is also marked as inconsistent.

recovery_tune_interval

  • Type: seconds
  • Default: 1
  • Can be changed online: yes

Interval at which OSD re-considers client and recovery load and automatically adjusts recovery_sleep_us. Recovery auto-tuning is disabled if recovery_tune_interval is set to 0.

Auto-tuning targets utilization. Utilization is a measure of load and is equal to the product of iops and average latency (so it may be greater than 1). You set "low" and "high" client utilization thresholds and two corresponding target recovery utilization levels. OSD calculates desired recovery utilization from client utilization using linear interpolation and auto-tunes recovery operation delay to make actual recovery utilization match desired.

This allows to reduce recovery/rebalance impact on client operations. It is of course impossible to remove it completely, but it should become adequate. In some tests rebalance could earlier drop client write speed from 1.5 GB/s to 50-100 MB/s, with default auto-tuning settings it now only reduces to ~1 GB/s.

recovery_tune_util_low

  • Type: number
  • Default: 0.1
  • Can be changed online: yes

Desired recovery/rebalance utilization when client load is high, i.e. when it is at or above recovery_tune_client_util_high.

recovery_tune_util_high

  • Type: number
  • Default: 1
  • Can be changed online: yes

Desired recovery/rebalance utilization when client load is low, i.e. when it is at or below recovery_tune_client_util_low.

recovery_tune_client_util_low

  • Type: number
  • Default: 0
  • Can be changed online: yes

Client utilization considered "low".

recovery_tune_client_util_high

  • Type: number
  • Default: 0.5
  • Can be changed online: yes

Client utilization considered "high".

recovery_tune_agg_interval

  • Type: integer
  • Default: 10
  • Can be changed online: yes

The number of last auto-tuning iterations to use for calculating the delay as average. Lower values result in quicker response to client load change, higher values result in more stable delay. Default value of 10 is usually fine.

recovery_tune_sleep_min_us

  • Type: microseconds
  • Default: 10
  • Can be changed online: yes

Minimum possible value for auto-tuned recovery_sleep_us. Lower values are changed to 0.

recovery_tune_sleep_cutoff_us

  • Type: microseconds
  • Default: 10000000
  • Can be changed online: yes

Maximum possible value for auto-tuned recovery_sleep_us. Higher values are treated as outliers and ignored in aggregation.