PFcache (Linuxcon, Seattle, 2015)

Denser containers with PFCache

Pavel EmelyanovContainerCon, Seattle, 2015

Agenda

How to store container files

Why shared template matters

What can be deduplicated and what should be

PFCache

Q&A

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FilesystemContainer
processes



FilesystemContainer
processes

Block deviceNetwork

Host
FilesystemHost
block deviceHardware


How to store container files (1)

FilesystemContainer
processes

Block deviceNetwork

Host
FilesystemHost

Chroot()Union FS



FilesystemContainer
processes

Block deviceNetwork

Host
FilesystemHost

Loop deviceZFS ZVolBTRFS subvolumePLoop


What's PLoop

Loop device plusAIO for better performance

Snapshots

QCOW2-like format for thin provisioning

Thin provisionong itself

Upstreaming work in progress



FilesystemContainer
processes

Block deviceNetwork

Host
FilesystemHost

LVMDM-thin



FilesystemContainer
processes

Block deviceNetwork

Host
FilesystemHost

NBDCeph RBDiSCSI



FilesystemContainer
processes

Block deviceNetwork

Host
FilesystemHost

NFSGFS2OCFSCeph


Containers vs Templates

Containers ...are massively cloned from pre-created templates

do not have direct access to the underlying (block) storage

Identical data can be effectively deduplicatedHigher density

Lower IO and/or memory consumption


Who can do shared templates

StorageOpenVZDockerLXC

Union FSs+++

Btrfs+DM-thin+PLoop+CephZFS+


What can be de-duplicated

FilesystemContainer
processes

Block deviceNetwork



FilesystemContainer
processes

Block deviceNetwork

Page cacheCached pages



FilesystemContainer
processes

Block deviceNetwork

Page cache

Cached pages

IO flow


What is deduplicated

StorageMemoryIO

Union FSs++

Btrfs+/-

DM-thinPLoop++

CephZFS


Additional OpenVZ constraints

Containers disks are independent image filesCan be easily copied across nodes

No single (shared) point of failure

Deduplicated data is volatileTemplates can be lost (e.g. while migrating)

Too big pool with shared data can be easily shrunk


Virtuozzo IO stack

Ext4Container
processes

PLoop device

Image file


PF-Cache

Ext4PLoop device

Cache area

Cache link (xattr)

Ext4Container
processes

PLoop device

Image file

Image file


Cache and cache link behavior

Cache areatarget file name is sha1 sum of the contents

files are created by user-space daemon

cache size is limited by ploop

Cache linkcreated automatically upon file creation

dropped when file is opened for writing

Is kept during metadata update (chown/chmod)


Density results


Future work

PLoop is available in OpenVZ & VirtuozzoUpstream WIP

IO deduplication in the upstreamIssue raied at 2013'th LSFMM

DM-thin/btrfs IO dedup for containers

KSM++ for VM-s


Thank [email protected]

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Software

PFcache (Linuxcon, Seattle, 2015)