![]() * l2arc_write_max max write bytes per interval * may be necessary for different workloads: * The performance of the L2ARC can be tweaked by a number of tunables, which * L2ARC, the now stale L2ARC buffer is immediately dropped. If an ARC buffer is written (and dirtied) which also exists in the * write buffers back to disk based storage. * device is written to in a rotor fashion, sweeping writes through * the vdev queue can aggregate them into larger and fewer writes. Writes to the L2ARC devices are grouped and sent in-sequence, so that * there are no L2ARC reads, and no fear of degrading read performance Since there have been no ARC evictions yet, * The L2ARC device write speed is also boosted during this time so that * for eligible buffers, greatly increasing its chance of finding them. * lists as pictured, the l2arc_feed_thread() will search from the list heads * no evictions from the ARC and so the tails of the ARC_mfu and ARC_mru After system boot and before the ARC has filled main memory, there are * quickly, such as during backups of the entire pool. * the potential for the L2ARC to churn if it attempts to cache content too * with waits and clogging the L2ARC with writes. * pressure valve to prevent heavy read workloads from both stalling the ARC * then the L2ARC simply misses copying some buffers. If the ARC evicts faster than the L2ARC can maintain a headroom, * the ARC lists have moved there due to inactivity. * safe to say that this is an uncommon case, since buffers at the end of * needed to, potentially wasting L2ARC device bandwidth and storage. * evicted, then the L2ARC has cached a buffer much sooner than it probably If an ARC buffer is copied to the L2ARC but then hit instead of * provide a better sense of ratio than this diagram: * l2arc_feed_thread(), illustrated below example sizes are included to * which itself is a buffer for ARC eviction. It scans until a headroom of buffers is satisfied, * the MFU and MRU ARC lists, copying them to the L2ARC devices if they are ![]() * It does this by periodically scanning buffers from the eviction-end of The L2ARC attempts to cache data from the ARC before it is evicted. * this would add inflated write latencies for all ARC memory pressure. The ARC does not send buffers to the L2ARC during eviction as * the ARC behave as usual, freeing buffers and placing headers on ghost There is no eviction path from the ARC to the L2ARC. * the L2ARC and traditional cache design: * To accommodate for this there are some significant differences between * Some L2ARC device types exhibit extremely slow write performance. * Read requests are satisfied from the following sources, in order: * substantially faster read latency than disk. * include short-stroked disks, solid state disks, and other media with * the performance of random read workloads. * It uses dedicated storage devices to hold cached data, which are populated * The level 2 ARC (L2ARC) is a cache layer in-between main memory and disk. Original comments inside Sun ZFS source code usr/src/uts/common/fs/zfs/arc.c on how L2ARC works. Reference: Level1Techs Forums – 27 Jan 22 e 'L1 deferred free' -e 'L0 deferred free' \ĮND ' \ e 'L1 SPA history' -e 'L0 SPA history' \ e '元 zvol object' -e 'L2 zvol object' -e 'L1 zvol object' -e 'L0 zvol object' \ e 'L2 ZFS directory' -e 'L1 ZFS directory' -e 'L0 ZFS directory' \ e 'L0 ZFS plain file' -e 'ZFS plain file' \ e 'L5 DMU dnode' -e 'L4 DMU dnode' -e '元 DMU dnode' -e 'L2 DMU dnode' -e 'L1 DMU dnode' -e 'L0 DMU dnode' \ e 'L2 SPA space map' -e 'L1 SPA space map' -e 'L0 SPA space map' \ e 'L1 object array' -e 'L0 object array' \ Sum the relevant sections in the ASIZE column ( Metadata Size INSIDE of Pool zdb -PLbbbs yourpool | tee ~/yourpool_metadata_output.txt Metadata Size OUTSIDE of Pool zpool list yourpool -vĢ. The comment at the end of that page is especially good at showing how to find a "good" tgx. There is a script called zfs_revert-0.1.py which follows a similar way of recovery. Mount it and dd some zeros to clear out the more recent bad tgx. Rollback to the good tgx zpool import -f -F -T If the above does not work, you will can try the really hardcore -T option and roll-back to a good tgx - this is not for the faint-hearted: If you cannot import a zpool, the following command might help: zpool import -FfmX draid Declustered RAID for ZFS Installation and Configuration Guide High Performance Data Division.pdf (1.8 MB).Chris's Wiki :: blog/solaris/ZFSLogicalVsPhysicalBlockSizes.Chris's Wiki :: blog/solaris/ZFSBlockPointers.OpenZFS can be tuned easily for almost every application.
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