Jul 10, 2015 · Since ZFS utilizes algorithms to track frequently used data in addition to recently used data, your cache devices will still provide performance improvements after a backup. ZFS brings frequently and recently used data to the highest performing storage, first to system memory, then to caching devices, allowing for flash media performance ...

Mar 24, 2022 · ARC/ZIL are terms used to describe ZFS’s ram cache. ARC is a read cache, much like the regular Unix caching mechanism, but where Unix typically uses a LRU algorithm, caching files that have been recently used, ARC uses a MRU algorithm, caching frequently used files. L2ARC handles overflow from the ARC, as in blocks evicted from the ARC cache.

Feb 18, 2025 · One is Adaptive Replacement Cache (ARC), which uses the server memory (RAM). The other is second level adaptive replacement cache (L2ARC), which uses cache drives added to ZFS storage pools. These cache drives are multi-level cell (MLC) SSD drives and, while slower than system memory, are still much faster than standard hard drives.

Mar 4, 2016 · To improve read performance, ZFS utilizes system memory as an Adaptive Replacement Cache (ARC), which stores your file system’s most frequently and recently used data in your system memory. You can then add a Level 2 Adaptive Replacement Cache (L2ARC) to extend the ARC to a dedicated disk (or disks) to dramatically improve read speeds ...

Sep 11, 2021 · zfs_arc_max; zfs_arc_sys_free; By default, TrueNAS has zfs_arc_max as 0, which defaults to 50%. zfs_arc_sys_free is interesting because it tells zfs to keep at least this much system memory free. I have combined these successfully since the …

Jun 27, 2023 · Just a correction, ZFS does not use memory (ram) as “traditional” write-back cache. This would create a risk for data integrity if a system lost power. Edit: Yes, ZFS coalesces writes in memory before flushing to disk but it doesn’t use it as a traditional “write back” cache.

May 5, 2020 · I have a question regarding zfs cache. It's nearly consuming 40Gb of RAM and bringing the system to a crawl. I wasn't aware ZFS cache consumed this much memory. Is there a way to limit the amount of RAM it requires since its basically making the system unusable. I have the following tunable: vfs.zfs.arc_max 61632000000 sysctl Generated by ...

Also whats about my ZFS-RAM usage: Can I expect to reduce it in that way? ZFS will try to use all RAM up to the specified limit. Changing pool config doesn't change this behaviour. In fact, since you now have to map the L2ARC data in RAM, you're increasing your RAM usage. This leaves less room to cache actual data in RAM, again slowing things down.

Nov 23, 2015 · ZFS cache and intent log don't necessarily help with the type of benchmarks you're running. ZIL is an intent log and mainly benefits synchronous writes (e.g. NFS exports from your ZFS server). In small installations, it won't help you. In ZFS, RAM is your write cache. L2ARC is a layer of cache, but requires time to warm up and populate.

Aug 25, 2021 · The way ZFS works: There is a read cache, ARC, in RAM. It can be increased in size with L2ARC in SSD, but get the ARC stats before you do: If your working set fits into ARC, there’s no point. There is a write cache in RAM, it can’t be increased in size. Notably SLOG is not a write cache, it’s for speeding up sync writes.