Some ZFS concepts Once again with no particular order of importance: ZFS Counterparts examples zpool A group of one or many physical storage media hard drive partition, file A zpool has to be divided in at least one ZFS dataset or at least one zvol to hold any data.
This means, that whatever L2ARC capacity you have installed, take the metadata overhead of it and that amount of data needs to be read in during rebuild. At a typical 0. Most solid state drives can transfer this kind of data volume within a second or two. However, given the structure of L2ARC pbufs, we don't know which pbuf to start fetching before we are done reading the current pbuf, and so we are also bound by the device's IOPS.
In practice, the implementation tries to alleviate these problems in two ways: By speculatively initiating a prefetch for the next pbuf when only the header of the current pbuf has been read so far. By executing the rebuild in a background thread for each L2ARC device in parallel.
To prevent malformed or damaged pbufs from sending the rebuild process into an unending cycle e. Exported kstats The following kstats were added to the arcstats set to provide additional information about persistent L2ARC performance: See the "Floating Averages and Ratios" section below for how these values are computed and updated.
Comparing these two numbers you can establish pbuf compression efficiency. For example, a value of "" means that for each bytes of data we consume 1 byte of metadata i.
Except for cases of device failure or serious data corruption, this number should track the above kstat. A non-zero value here indicates that your L2ARC device is either very slow or is failing.
Otherwise, it should be precisely equal. This is the first step taken during L2ARC rebuild.
Any non-zero value here indicates a failing L2ARC device. This is a serious condition and indicates severely corrupted L2ARC metadata. You may want to try to re-add the L2ARC device at a later time when the memory pressure is relieved, in order to rebuild the L2ARC device's complete contents.
Floating Averages and Ratios Due to the fact that we don't keep a history of L2ARC metadata we write in memory, it is difficult compute certain aggregate averages and ratio values.
Instead, we compute a "floating statistic", which tracks the recent history of the statistic by slowly factoring in individual updates to it, which is very similar to how load average track system load.
We do this by applying the following formula:Jul 23, · Future of ZFS Discussion in 'Storage' started by Thanks Received: 0 Trophy Points: 4 Location: New Westminster, Canada.
Now that Oracle has apparently decided to move future ZFS development from being open to closed and proprietary source does anyone know where we are going from here?
I was hungry for that block pointer rewrite. Welcome to this year's 35th issue of DistroWatch Weekly! While most of our reviews tend to focus on major and reasonably well-known distributions, it's good to take a look at lesser ones every now and then. Finally. we will try to implement quazi-write cache with ZFS Intent Log (ZIL) forcing it to handle both types of synchronous and asynchronous transactions and write them to the shared drive da0 (the ctrl-a_m0 pool on the ctrl-a controller) and da2 (ctrl-b_m0 pool on on the ctrl-b): ctrl-a zpool add ctrl-a_m0 log /dev/da0 # Always write and.
Initial patch by Dan timberdesignmag.com() is defined to returned None when the call would block..
including adjacent and unquoted timberdesignmag.com now uses the repr() for floats rather than str(). ZFS is missing a "block pointer rewrite functionality", true on all known implementations so far.
Not a major performance crippling however. BTRFS can do on-line data defragmentation. Pools and their associated ZFS file systems can be moved between different platform architectures, including systems implementing different byte orders.
The ZFS block pointer format stores filesystem metadata in an endian-adaptive way; individual metadata blocks are written with the native byte order of the system writing the block.
When reading, if the stored endianness does not match the endianness of .