BlueStore Config Reference¶
Devices¶
BlueStore manages either one, two, or (in certain cases) three storage devices.
In the simplest case, BlueStore consumes a single (primary) storage device.
The storage device is normally used as a whole, occupying the full device that
is managed directly by BlueStore. This primary device is normally identified
by a block
symlink in the data directory.
The data directory is a tmpfs
mount which gets populated (at boot time, or
when ceph-volume
activates it) with all the common OSD files that hold
information about the OSD, like: its identifier, which cluster it belongs to,
and its private keyring.
It is also possible to deploy BlueStore across two additional devices:
A WAL device (identified as
block.wal
in the data directory) can be used for BlueStore’s internal journal or write-ahead log. It is only useful to use a WAL device if the device is faster than the primary device (e.g., when it is on an SSD and the primary device is an HDD).A DB device (identified as
block.db
in the data directory) can be used for storing BlueStore’s internal metadata. BlueStore (or rather, the embedded RocksDB) will put as much metadata as it can on the DB device to improve performance. If the DB device fills up, metadata will spill back onto the primary device (where it would have been otherwise). Again, it is only helpful to provision a DB device if it is faster than the primary device.
If there is only a small amount of fast storage available (e.g., less than a gigabyte), we recommend using it as a WAL device. If there is more, provisioning a DB device makes more sense. The BlueStore journal will always be placed on the fastest device available, so using a DB device will provide the same benefit that the WAL device would while also allowing additional metadata to be stored there (if it will fit).
A single-device BlueStore OSD can be provisioned with:
ceph-volume lvm prepare --bluestore --data <device>
To specify a WAL device and/or DB device,
ceph-volume lvm prepare --bluestore --data <device> --block.wal <wal-device> --block.db <db-device>
Note
–data can be a Logical Volume using the vg/lv notation. Other devices can be existing logical volumes or GPT partitions
Provisioning strategies¶
Although there are multiple ways to deploy a Bluestore OSD (unlike Filestore which had 1) here are two common use cases that should help clarify the initial deployment strategy:
block (data) only¶
If all the devices are the same type, for example all are spinning drives, and
there are no fast devices to combine these, it makes sense to just deploy with
block only and not try to separate block.db
or block.wal
. The
lvm call for a single /dev/sda
device would look like:
ceph-volume lvm create --bluestore --data /dev/sda
If logical volumes have already been created for each device (1 LV using 100%
of the device), then the lvm call for an lv named
ceph-vg/block-lv
would look like:
ceph-volume lvm create --bluestore --data ceph-vg/block-lv
block and block.db¶
If there is a mix of fast and slow devices (spinning and solid state),
it is recommended to place block.db
on the faster device while block
(data) lives on the slower (spinning drive). Sizing for block.db
should be
as large as possible to avoid performance penalties otherwise. The
ceph-volume
tool is currently not able to create these automatically, so
the volume groups and logical volumes need to be created manually.
For the below example, lets assume 4 spinning drives (sda, sdb, sdc, and sdd) and 1 solid state drive (sdx). First create the volume groups:
$ vgcreate ceph-block-0 /dev/sda
$ vgcreate ceph-block-1 /dev/sdb
$ vgcreate ceph-block-2 /dev/sdc
$ vgcreate ceph-block-3 /dev/sdd
Now create the logical volumes for block
:
$ lvcreate -l 100%FREE -n block-0 ceph-block-0
$ lvcreate -l 100%FREE -n block-1 ceph-block-1
$ lvcreate -l 100%FREE -n block-2 ceph-block-2
$ lvcreate -l 100%FREE -n block-3 ceph-block-3
We are creating 4 OSDs for the four slow spinning devices, so assuming a 200GB
SSD in /dev/sdx
we will create 4 logical volumes, each of 50GB:
$ vgcreate ceph-db-0 /dev/sdx
$ lvcreate -L 50GB -n db-0 ceph-db-0
$ lvcreate -L 50GB -n db-1 ceph-db-0
$ lvcreate -L 50GB -n db-2 ceph-db-0
$ lvcreate -L 50GB -n db-3 ceph-db-0
Finally, create the 4 OSDs with ceph-volume
:
$ ceph-volume lvm create --bluestore --data ceph-block-0/block-0 --block.db ceph-db-0/db-0
$ ceph-volume lvm create --bluestore --data ceph-block-1/block-1 --block.db ceph-db-0/db-1
$ ceph-volume lvm create --bluestore --data ceph-block-2/block-2 --block.db ceph-db-0/db-2
$ ceph-volume lvm create --bluestore --data ceph-block-3/block-3 --block.db ceph-db-0/db-3
These operations should end up creating 4 OSDs, with block
on the slower
spinning drives and a 50GB logical volume for each coming from the solid state
drive.
Sizing¶
When using a mixed spinning and solid drive setup it is important to make a large-enough
block.db
logical volume for Bluestore. Generally, block.db
should have
as large as possible logical volumes.
It is recommended that the block.db
size isn’t smaller than 4% of
block
. For example, if the block
size is 1TB, then block.db
shouldn’t be less than 40GB.
If not using a mix of fast and slow devices, it isn’t required to create
separate logical volumes for block.db
(or block.wal
). Bluestore will
automatically manage these within the space of block
.
Automatic Cache Sizing¶
Bluestore can be configured to automatically resize it’s caches when tc_malloc
is configured as the memory allocator and the bluestore_cache_autotune
setting is enabled. This option is currently enabled by default. Bluestore
will attempt to keep OSD heap memory usage under a designated target size via
the osd_memory_target
configuration option. This is a best effort
algorithm and caches will not shrink smaller than the amount specified by
osd_memory_cache_min
. Cache ratios will be chosen based on a hierarchy
of priorities. If priority information is not availabe, the
bluestore_cache_meta_ratio
and bluestore_cache_kv_ratio
options are
used as fallbacks.
bluestore_cache_autotune
- Description
Automatically tune the ratios assigned to different bluestore caches while respecting minimum values.
- Type
Boolean
- Required
Yes
- Default
True
osd_memory_target
- Description
When tcmalloc is available and cache autotuning is enabled, try to keep this many bytes mapped in memory. Note: This may not exactly match the RSS memory usage of the process. While the total amount of heap memory mapped by the process should generally stay close to this target, there is no guarantee that the kernel will actually reclaim memory that has been unmapped. During initial developement, it was found that some kernels result in the OSD’s RSS Memory exceeding the mapped memory by up to 20%. It is hypothesised however, that the kernel generally may be more aggressive about reclaiming unmapped memory when there is a high amount of memory pressure. Your mileage may vary.
- Type
Unsigned Integer
- Required
Yes
- Default
4294967296
bluestore_cache_autotune_chunk_size
- Description
The chunk size in bytes to allocate to caches when cache autotune is enabled. When the autotuner assigns memory to different caches, it will allocate memory in chunks. This is done to avoid evictions when there are minor fluctuations in the heap size or autotuned cache ratios.
- Type
Unsigned Integer
- Required
No
- Default
33554432
bluestore_cache_autotune_interval
- Description
The number of seconds to wait between rebalances when cache autotune is enabled. This setting changes how quickly the ratios of the difference caches are recomputed. Note: Setting the interval too small can result in high CPU usage and lower performance.
- Type
Float
- Required
No
- Default
5
osd_memory_base
- Description
When tcmalloc and cache autotuning is enabled, estimate the minimum amount of memory in bytes the OSD will need. This is used to help the autotuner estimate the expected aggregate memory consumption of the caches.
- Type
Unsigned Interger
- Required
No
- Default
805306368
osd_memory_expected_fragmentation
- Description
When tcmalloc and cache autotuning is enabled, estimate the percent of memory fragmentation. This is used to help the autotuner estimate the expected aggregate memory consumption of the caches.
- Type
Float
- Required
No
- Default
0.15
osd_memory_cache_min
- Description
When tcmalloc and cache autotuning is enabled, set the minimum amount of memory used for caches. Note: Setting this value too low can result in significant cache thrashing.
- Type
Unsigned Integer
- Required
No
- Default
134217728
osd_memory_cache_resize_interval
- Description
When tcmalloc and cache autotuning is enabled, wait this many seconds between resizing caches. This setting changes the total amount of memory available for bluestore to use for caching. Note: Setting the interval too small can result in memory allocator thrashing and lower performance.
- Type
Float
- Required
No
- Default
1
Manual Cache Sizing¶
The amount of memory consumed by each OSD for BlueStore’s cache is
determined by the bluestore_cache_size
configuration option. If
that config option is not set (i.e., remains at 0), there is a
different default value that is used depending on whether an HDD or
SSD is used for the primary device (set by the
bluestore_cache_size_ssd
and bluestore_cache_size_hdd
config
options).
BlueStore and the rest of the Ceph OSD does the best it can currently to stick to the budgeted memory. Note that on top of the configured cache size, there is also memory consumed by the OSD itself, and generally some overhead due to memory fragmentation and other allocator overhead.
The configured cache memory budget can be used in a few different ways:
Key/Value metadata (i.e., RocksDB’s internal cache)
BlueStore metadata
BlueStore data (i.e., recently read or written object data)
Cache memory usage is governed by the following options:
bluestore_cache_meta_ratio
and bluestore_cache_kv_ratio
.
The fraction of the cache devoted to data
is governed by the effective bluestore cache size (depending on
bluestore_cache_size[_ssd|_hdd]
settings and the device class of the primary
device) as well as the meta and kv ratios.
The data fraction can be calculated by
<effective_cache_size> * (1 - bluestore_cache_meta_ratio - bluestore_cache_kv_ratio)
bluestore_cache_size
- Description
The amount of memory BlueStore will use for its cache. If zero,
bluestore_cache_size_hdd
orbluestore_cache_size_ssd
will be used instead.- Type
Unsigned Integer
- Required
Yes
- Default
0
bluestore_cache_size_hdd
- Description
The default amount of memory BlueStore will use for its cache when backed by an HDD.
- Type
Unsigned Integer
- Required
Yes
- Default
1 * 1024 * 1024 * 1024
(1 GB)
bluestore_cache_size_ssd
- Description
The default amount of memory BlueStore will use for its cache when backed by an SSD.
- Type
Unsigned Integer
- Required
Yes
- Default
3 * 1024 * 1024 * 1024
(3 GB)
bluestore_cache_meta_ratio
- Description
The ratio of cache devoted to metadata.
- Type
Floating point
- Required
Yes
- Default
.4
bluestore_cache_kv_ratio
- Description
The ratio of cache devoted to key/value data (rocksdb).
- Type
Floating point
- Required
Yes
- Default
.4
bluestore_cache_kv_max
- Description
The maximum amount of cache devoted to key/value data (rocksdb).
- Type
Unsigned Integer
- Required
Yes
- Default
512 * 1024*1024
(512 MB)
Checksums¶
BlueStore checksums all metadata and data written to disk. Metadata checksumming is handled by RocksDB and uses crc32c. Data checksumming is done by BlueStore and can make use of crc32c, xxhash32, or xxhash64. The default is crc32c and should be suitable for most purposes.
Full data checksumming does increase the amount of metadata that BlueStore must store and manage. When possible, e.g., when clients hint that data is written and read sequentially, BlueStore will checksum larger blocks, but in many cases it must store a checksum value (usually 4 bytes) for every 4 kilobyte block of data.
It is possible to use a smaller checksum value by truncating the checksum to two or one byte, reducing the metadata overhead. The trade-off is that the probability that a random error will not be detected is higher with a smaller checksum, going from about one in four billion with a 32-bit (4 byte) checksum to one in 65,536 for a 16-bit (2 byte) checksum or one in 256 for an 8-bit (1 byte) checksum. The smaller checksum values can be used by selecting crc32c_16 or crc32c_8 as the checksum algorithm.
The checksum algorithm can be set either via a per-pool
csum_type
property or the global config option. For example,
ceph osd pool set <pool-name> csum_type <algorithm>
bluestore_csum_type
- Description
The default checksum algorithm to use.
- Type
String
- Required
Yes
- Valid Settings
none
,crc32c
,crc32c_16
,crc32c_8
,xxhash32
,xxhash64
- Default
crc32c
Inline Compression¶
BlueStore supports inline compression using snappy, zlib, or lz4. Please note that the lz4 compression plugin is not distributed in the official release.
Whether data in BlueStore is compressed is determined by a combination of the compression mode and any hints associated with a write operation. The modes are:
none: Never compress data.
passive: Do not compress data unless the write operation has a compressible hint set.
aggressive: Compress data unless the write operation has an incompressible hint set.
force: Try to compress data no matter what.
For more information about the compressible and incompressible IO
hints, see rados_set_alloc_hint()
.
Note that regardless of the mode, if the size of the data chunk is not
reduced sufficiently it will not be used and the original
(uncompressed) data will be stored. For example, if the bluestore
compression required ratio
is set to .7
then the compressed data
must be 70% of the size of the original (or smaller).
The compression mode, compression algorithm, compression required ratio, min blob size, and max blob size can be set either via a per-pool property or a global config option. Pool properties can be set with:
ceph osd pool set <pool-name> compression_algorithm <algorithm>
ceph osd pool set <pool-name> compression_mode <mode>
ceph osd pool set <pool-name> compression_required_ratio <ratio>
ceph osd pool set <pool-name> compression_min_blob_size <size>
ceph osd pool set <pool-name> compression_max_blob_size <size>
bluestore compression algorithm
- Description
The default compressor to use (if any) if the per-pool property
compression_algorithm
is not set. Note that zstd is not recommended for bluestore due to high CPU overhead when compressing small amounts of data.- Type
String
- Required
No
- Valid Settings
lz4
,snappy
,zlib
,zstd
- Default
snappy
bluestore compression mode
- Description
The default policy for using compression if the per-pool property
compression_mode
is not set.none
means never use compression.passive
means use compression whenclients hint
that data is compressible.aggressive
means use compression unless clients hint that data is not compressible.force
means use compression under all circumstances even if the clients hint that the data is not compressible.- Type
String
- Required
No
- Valid Settings
none
,passive
,aggressive
,force
- Default
none
bluestore compression required ratio
- Description
The ratio of the size of the data chunk after compression relative to the original size must be at least this small in order to store the compressed version.
- Type
Floating point
- Required
No
- Default
.875
bluestore compression min blob size
- Description
Chunks smaller than this are never compressed. The per-pool property
compression_min_blob_size
overrides this setting.- Type
Unsigned Integer
- Required
No
- Default
0
bluestore compression min blob size hdd
- Description
Default value of
bluestore compression min blob size
for rotational media.- Type
Unsigned Integer
- Required
No
- Default
128K
bluestore compression min blob size ssd
- Description
Default value of
bluestore compression min blob size
for non-rotational (solid state) media.- Type
Unsigned Integer
- Required
No
- Default
8K
bluestore compression max blob size
- Description
Chunks larger than this are broken into smaller blobs sizing
bluestore compression max blob size
before being compressed. The per-pool propertycompression_max_blob_size
overrides this setting.- Type
Unsigned Integer
- Required
No
- Default
0
bluestore compression max blob size hdd
- Description
Default value of
bluestore compression max blob size
for rotational media.- Type
Unsigned Integer
- Required
No
- Default
512K
bluestore compression max blob size ssd
- Description
Default value of
bluestore compression max blob size
for non-rotational (solid state) media.- Type
Unsigned Integer
- Required
No
- Default
64K
SPDK Usage¶
If you want to use SPDK driver for NVME SSD, you need to ready your system. Please refer to SPDK document for more details.
SPDK offers a script to configure the device automatically. Users can run the script as root:
$ sudo src/spdk/scripts/setup.sh
Then you need to specify NVMe device’s device selector here with “spdk:” prefix for
bluestore_block_path
.
For example, users can find the device selector of an Intel PCIe SSD with:
$ lspci -mm -n -D -d 8086:0953
The device selector always has the form of DDDD:BB:DD.FF
or DDDD.BB.DD.FF
.
and then set:
bluestore block path = spdk:0000:01:00.0
Where 0000:01:00.0
is the device selector found in the output of lspci
command above.
If you want to run multiple SPDK instances per node, you must specify the amount of dpdk memory size in MB each instance will use, to make sure each instance uses its own dpdk memory
In most cases, we only need one device to serve as data, db, db wal purposes. We need to make sure configurations below to make sure all IOs issued under SPDK.:
bluestore_block_db_path = ""
bluestore_block_db_size = 0
bluestore_block_wal_path = ""
bluestore_block_wal_size = 0
Otherwise, the current implementation will setup symbol file to kernel filesystem location and uses kernel driver to issue DB/WAL IO.