Default options

Ceph creates images with the 2 format and with no striping.

Table 1 lists the different default options for Ceph Block Device configuration.
Note: The default settings can be overridden.
Table 1. Ceph Block Device default options
Option Description Type Default Notes
rbd_default_format The default format (2) if no other format is specified. Format 1 is the original format for a new image, which is compatible with all versions of librbd and the kernel module, but does not support newer features like cloning. Format 2 is supported by librbd and the kernel module since version 3.11 (except for striping). Format 2 adds support for cloning and is more easily extensible to allow more features in the future. Integer 2
rbd_default_order The default order if no other order is specified. Integer 22
rbd_default_stripe_count The default stripe count if no other stripe count is specified. Changing the default value requires striping v2 feature. 64-bit Unsigned Integer 0
rbd_default_stripe_unit The default stripe unit if no other stripe unit is specified. Changing the unit from 0 (that is, the object size) requires the striping v2 feature. 64-bit Unsigned Integer 0
rbd_default_features The default features enabled when creating a block device image. The settings only apply to format two images. The settings are as follows:
1: Layering support
Layering enables you to use cloning.
2:Striping v2 support
Striping spreads data across multiple objects. Striping helps with parallelism for sequential read/write workloads.
4: Exclusive locking support
When enabled, it requires a client to get a lock on an object before making a write.
8: Object map support
Block devices are thin-provisioned—​meaning, they only store data that actually exists. Object map support helps track which objects actually exist (have data stored on a drive). Enabling object map support speeds up I/O operations for cloning, or importing and exporting a sparsely populated image.
16: Fast-diff support
Fast-diff support depends on object map support and exclusive lock support. It adds another property to the object map, which makes it much faster to generate diffs between snapshots of an image, and the actual data usage of a snapshot much faster.
32: Deep-flatten support
Deep-flatten makes rbd flatten work on all the snapshots of an image, in addition to the image itself. Without it, snapshots of an image will still rely on the parent, so the parent will not be delete-able until the snapshots are deleted. Deep-flatten makes a parent independent of its clones, even if they have snapshots.
64: Journaling support
Journaling records all modifications to an image in the order they occur. This ensures that a crash-consistent mirror of the remote image is available locally.
The enabled features are the sum of the numeric settings.		 Integer 61 Layering, exclusive-lock, object-map, fast-diff, and deep-flatten are enabled.
Important: The current default setting is not compatible with the RADOS Block Device kernel driver or older RADOS Block Device clients.
rbd_default_map_options Most of the options are useful mainly for debugging and benchmarking. For more information, see man rbd under Map Options. String ""