63f8a472af
(I will give a talk on this PoC at the OpenZFS Developer Summit 2022.) The ARC dynamically shares DRAM capacity among all currently imported zpools. However, the L2ARC does not do the same for block capacity: the L2ARC vdevs of one zpool only cache buffers of that zpool. This can be undesirable on systems that host multiple zpools because it inhibits dynamic sharing of the cache device capacity which is desirable if the need for L2ARC varies among zpools over time, or if the set of zpools that are imported in the system varies over time. Shared L2ARC addresses this need by decoupling the L2ARC vdevs from the zpools that store actual data. The mechanism that we use is to place the L2ARC vdevs into a special zpool, and to adjust the L2ARC feed thread logic to use that special zpool's L2ARC vdevs for all zpools' buffers. High-level changes: * Reserve "NTNX-fsvm-local-l2arc" as a magic zpool name. We call this "the l2arc pool". All other pools are called "primary pools". * Make l2arc feed thread feed ARC buffers from any zpool to the l2arc zpool. (Before this patch, the l2arc feed thread would only feed ARC buffers to l2arc devices if they are for the same spa_t). * Change the locking to ensure that the l2arc zpool cannot be removed while there are ongoing reads initiated by arc_read on one of the primary pools. This is sufficient and retains correctness of the ARC because nothing about the fundamental operation of L2ARC changes. The only thing that changes is that the L2ARC data is stored on vdevs outside the primary pool. Proof Of Concept => Production ============================== This commit is a proof-of-concept. It works, it results in the desired performance improvement, and it's stable. But to make it production ready, more work needs to be done. (1) The design is based on a version of ZFS that does not support encryption nor Persisent L2ARC. I'm no expert in either of these features. Encryption might work just fine as long as the l2arc feed thread can access the encryption keys for l2arc_apply_transforms. But Persistent L2ARC definitely needs more design work (multiple L2ARC headers?). (2) Remove hard-coded magic name; use a property instead. Make it opt-in so that existing setups are not affected. Example: zpool create -o share_l2arc_vdevs=on my-l2arc-pool (3) Coexistence with non-shared L2ARC; also via property. Make it opt-in so that existing setups are not affected. Example: zpool set use_shared_l2arc=on my-data-pool Signed-off-by: Christian Schwarz <christian.schwarz@nutanix.com> |
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README.md
OpenZFS is an advanced file system and volume manager which was originally developed for Solaris and is now maintained by the OpenZFS community. This repository contains the code for running OpenZFS on Linux and FreeBSD.
Official Resources
- Documentation - for using and developing this repo
- ZoL Site - Linux release info & links
- Mailing lists
- OpenZFS site - for conference videos and info on other platforms (illumos, OSX, Windows, etc)
Installation
Full documentation for installing OpenZFS on your favorite operating system can be found at the Getting Started Page.
Contribute & Develop
We have a separate document with contribution guidelines.
We have a Code of Conduct.
Release
OpenZFS is released under a CDDL license.
For more details see the NOTICE, LICENSE and COPYRIGHT files; UCRL-CODE-235197
Supported Kernels
- The
METAfile contains the officially recognized supported Linux kernel versions. - Supported FreeBSD versions are any supported branches and releases starting from 12.2-RELEASE.