DragonFly BSD

features

DragonFly's Major Features List

KERNEL

Please keep in mind that major modifications have been made to nearly the entire DragonFly kernel relative to the original FreeBSD-4.x fork. Significant changes have been made to every kernel subsystem, as a consequence this list is constrained to the largest, most user-visible changes unique to DragonFly.

HAMMER - DragonFly Filesystem

HAMMER is the DragonFly filesystem, replacing UFS. HAMMER supports up to an Exabyte of storage, implements a fast UNDO/REDO FIFO for fsync(), recovers instantly on boot after a crash (no fsck), and implements a very sophisticated fine-grained historical access and snapshot mechanism. HAMMER also sports an extremely robust streaming, queueless master->multiple-slave mirroring capability which is also able to mirror snapshots and other historical data.

All non-temporary HAMMER filesystems in DragonFly automatically maintain 60 days worth of 1-day snapshots and 1-day worth of fine-grained (30-second) snapshots.

HAMMER is designed to accommodate today's large drives.

NULLFS - NULL Filesystem Layer

A null or loop-back filesystem is common to a number of operating systems. The DragonFly null filesystem is quite a different animal. It supports arbitrary mount points that do not loop, a problem on other operating systems, making it extremely flexible in its application. It is also extremely fast and reliable, something that few other operating systems can claim of their null filesystem layers.

TMPFS - Temporary FileSystem VFS

Originally a NetBSD port the guts have been radically adjusted and carefully tuned to provide a low-contention read path and to directly tie the backing store to the VM/paging system in a way that treats it almost like normal memory. Only memory pressure will force tmpfs data pages into swap.

TMPFS replaces MFS and MD (for post-boot use).

DM_TARGET_CRYPT, TCPLAY - Transparent disk encryption

DragonFly has a device mapper target called dm_target_crypt (compatible with Linux' dm-crypt) that provides transparent disk encryption. It makes best use of available cryptographic hardware, as well as multi-processor software crypto.

DragonFly fully supports LUKS (cryptsetup) and TrueCrypt as disk encryption methods. tcplay, is a free (BSD-licensed) 100% compatible TrueCrypt implementation built on dm_target_crypt.

SWAPCACHE - Managed SSD support

This DragonFly feature allows SSD-configured swap to also be used to cache clean filesystem data and meta-data. The feature is carefully managed to maximize the write endurance of the SSD. Swapcache is typically used to reduce or remove seek overheads related to managing filesystems with a large number of discrete inodes. DragonFly's swap subsystem also supports much larger than normal swap partitions. 32-bit systems support 32G of swap by default while 64-bit systems support up to 512G of swap by default.

VARIANT SYMLINKS

Variant (context-sensitive) symlinks give users, administrators and application authors an extremely useful tool to aid in configuration and management. Special varsym variables can be used within an otherwise conventional symbolic link and resolved at run-time.

PROCESS CHECKPOINTING

Processes under DragonFly may be "checkpointed" or suspended to disk at any time. They may later be resumed on the originating system, or another system by "thawing" them.

DNTPD - DragonFly Network Time Daemon

DragonFly has its own from-scratch time daemon. After pulling our hair out over the many issues with open source time daemons we decided to write one ourselves and add new system calls to support it. DNTPD uses a double staggered linear regression and correlation to make time corrections. It will also properly deal with network failures (including lack of connectivity on boot), duplicate IPs resolved by DNS, and time source failures (typically 1 second off) when multiple time sources are available. The linear regression and correlation allows DNTPD to make rough adjustments and frequency corrections within 5 minutes of boot and to make more fine-grained adjustments at any time following when the linear regression indicates accuracy beyond the noise floor.

DMA - DragonFly Mail Agent

The DragonFly Mail Agent is a bare-bones (though not so bare-bones any more) mail transfer and mail terminus SMTP server which provides all the functionality needed for local mail delivery and simple remote mail transfers. A more sophisticated MTA can then be thrown onto an installed system via DPorts.