When testing with UDP, no changes are required on the server side. Continue using iperf3 -s to run the server. See below. This is pretty normal. The TCP protocol checks each time to make sure the target recieved the packets that the origin sent. UDP on the other hand, just sends packets like a crazy person.
UDP just wants to send packets quickly. UDP is most commonly used for video streaming services. There is no error correction with UDP. You may run into a situation where you want to run iPerf on a different port. This is pretty easily done by adding the -p flag. You will need to do this on both the client and the server. Daemon mode is used when you want to keep your iPerf Server up and running without having to SSH in each time to start it up. There are no changes to the client side when running in this configuration.
Just connect as you normally would from the iPerf Client. The obvious solution is to use the ps command. We can cat that file to get the iPerf PID. Pretty useful feature if you are looking to automate iPerf or need a way for a monitoring check to see if iPerf is still running.
Eventually you will probably want to stop the iPerf Server running in Daemon Mode. This is as simple as running pkill iperf. You could also use the PID file you just learned how to make. Here is a quick one-liner to kill iPerf if you are using a PID file. You can subscribe to my mailing list below or follow me on Twitter if you want me to notify you when I make a new post. You can also Buy Me A Coffee to help keep me going!
As an Amazon Associate I earn from qualifying purchases. Adjust this value to prevent other applications from pressuring out the entire ARC. The total amount of memory used will be this value multiplied by the number of devices. The value is a power of two. To avoid write amplification and get the best performance, set this value to the largest sector size used by a device in the pool.
Common drives have 4 KB sectors. Using the default ashift of 9 with these drives results in write amplification on these devices. Data contained in a single 4 KB write is instead written in eight byte writes.
ZFS tries to read the native sector size from all devices when creating a pool, but drives with 4 KB sectors report that their sectors are bytes for compatibility.
Setting vfs. Forcing 4 KB blocks is also useful on pools with planned disk upgrades. Future disks use 4 KB sectors, and ashift values cannot change after creating a pool. In some specific cases, the smaller byte block size might be preferable. When used with byte disks for databases or as storage for virtual machines, less data transfers during small random reads. This can provide better performance when using a smaller ZFS record size. A value of 0 enables and 1 disables it. Prefetch works by reading larger blocks than requested into the ARC in hopes to soon need the data.
If the workload has a large number of random reads, disabling prefetch may actually improve performance by reducing unnecessary reads. Adjust this value at any time with sysctl 8. This ensures the best performance and longevity for SSDs, but takes extra time. If the device has already been secure erased, disabling this setting will make the addition of the new device faster. A higher value will keep the device command queue full and may give higher throughput.
A lower value will reduce latency. Limits the depth of the command queue to prevent high latency. The limit is per top-level vdev, meaning the limit applies to each mirror , RAID-Z , or other vdev independently.
This tunable extends the longevity of SSDs by limiting the amount of data written to the device. The granularity of the setting is determined by the value of kern. Changing this setting results in a different effective IOPS limit. Recent activity on the pool limits the speed of scrub , as determined by vfs.
ZFS determins the granularity of the setting by the value of kern. Returning the pool to an Online state may be more important if another device failing could Fault the pool, causing data loss.
A value of 0 will give the resilver operation the same priority as other operations, speeding the healing process. Other recent activity on the pool limits the speed of resilver, as determined by vfs. ZFS disables the rate limiting for scrub and resilver when the pool is idle. The current transaction group writes to the pool and a fresh transaction group starts if this amount of time elapsed since the previous transaction group.
A transaction group may trigger earlier if writing enough data. The default value is 5 seconds. A larger value may improve read performance by delaying asynchronous writes, but this may cause uneven performance when writing the transaction group.
Some of the features provided by ZFS are memory intensive, and may require tuning for upper efficiency on systems with limited RAM. As a lower value, the total system memory should be at least one gigabyte. This expands the kernel address space, allowing the vm. To find the most suitable value for this option, divide the desired address space in megabytes by four. In this example for 2 GB. Increases the kmem address space on all FreeBSD architectures. More than a file system, ZFS is fundamentally different.
ZFS combines the roles of file system and volume manager, enabling new storage devices to add to a live system and having the new space available on the existing file systems in that pool at once. By combining the traditionally separate roles, ZFS is able to overcome previous limitations that prevented RAID groups being able to grow.
ZFS file systems called datasets each have access to the combined free space of the entire pool. Used blocks from the pool decrease the space available to each file system. This approach avoids the common pitfall with extensive partitioning where free space becomes fragmented across the partitions.
A storage pool is the most basic building block of ZFS. A pool consists of one or more vdevs, the underlying devices that store the data. A pool is then used to create one or more file systems datasets or block devices volumes.
These datasets and volumes share the pool of remaining free space. Each pool is uniquely identified by a name and a GUID. The ZFS version number on the pool determines the features available.
A pool consists of one or more vdevs, which themselves are a single disk or a group of disks, transformed to a RAID. When using a lot of vdevs, ZFS spreads data across the vdevs to increase performance and maximize usable space. All vdevs must be at least MB in size. Disk - The most basic vdev type is a standard block device.
On FreeBSD, there is no performance penalty for using a partition rather than the entire disk. This differs from recommendations made by the Solaris documentation. Using an entire disk as part of a bootable pool is strongly discouraged, as this may render the pool unbootable.
File - Regular files may make up ZFS pools, which is useful for testing and experimentation. Use the full path to the file as the device path in zpool create. Mirror - When creating a mirror, specify the mirror keyword followed by the list of member devices for the mirror. A mirror consists of two or more devices, writing all data to all member devices. A mirror vdev will hold as much data as its smallest member. A mirror vdev can withstand the failure of all but one of its members without losing any data.
To upgrade a regular single disk vdev to a mirror vdev at any time, use zpool attach. If another disk goes offline before replacing and resilvering the faulted disk would result in losing all pool data. If more disks make up the configuration, the recommendation is to divide them into separate vdevs and stripe the pool data across them. Spare - ZFS has a special pseudo-vdev type for keeping track of available hot spares. Note that installed hot spares are not deployed automatically; manually configure them to replace the failed device using zfs replace.
Having a dedicated log device improves the performance of applications with a high volume of synchronous writes like databases. If using a lot of log devices, writes will be load-balanced across them. Mirroring cache devices is impossible. Since a cache device stores only new copies of existing data, there is no risk of data loss.
Transaction Groups are the way ZFS groups blocks changes together and writes them to the pool. Transaction groups are the atomic unit that ZFS uses to ensure consistency. ZFS assigns each transaction group a unique bit consecutive identifier.
There can be up to three active transaction groups at a time, one in each of these three states:. There is always a transaction group in the open state, but the transaction group may refuse new writes if it has reached a limit. Once the open transaction group has reached a limit, or reaching the vfs. Once all the transactions in the group have completed, the transaction group advances to the final state.
This process will in turn change other data, such as metadata and space maps, that ZFS will also write to stable storage.
The process of syncing involves several passes. On the first and biggest, all the changed data blocks; next come the metadata, which may take several passes to complete. Since allocating space for the data blocks generates new metadata, the syncing state cannot finish until a pass completes that does not use any new space.
The syncing state is also where synctasks complete. Synctasks are administrative operations such as creating or destroying snapshots and datasets that complete the uberblock change. Once the sync state completes the transaction group in the quiescing state advances to the syncing state.
All administrative functions, such as snapshot write as part of the transaction group. ZFS adds a created synctask to the open transaction group, and that group advances as fast as possible to the syncing state to reduce the latency of administrative commands.
An LRU cache is a simple list of items in the cache, sorted by how recently object was used, adding new items to the head of the list. When the cache is full, evicting items from the tail of the list makes room for more active objects. These ghost lists track evicted objects to prevent adding them back to the cache. This increases the cache hit ratio by avoiding objects that have a history of occasional use. With ZFS, there is also an MFU that tracks the most frequently used objects, and the cache of the most commonly accessed blocks remains.
Solid State Disks SSDs are often used as these cache devices due to their higher speed and lower latency compared to traditional spinning disks. L2ARC is entirely optional, but having one will increase read speeds for cached files on the SSD instead of having to read from the regular disks.
Limits on the data rate added to the cache devices prevents prematurely wearing out SSDs with extra writes. Until the cache is full the first block evicted to make room , writes to the L2ARC limit to the sum of the write limit and the boost limit, and afterwards limit to the write limit.
A pair of sysctl 8 values control these rate limits. ZIL accelerates synchronous transactions by using storage devices like SSDs that are faster than those used in the main storage pool. When an application requests a synchronous write a guarantee that the data is stored to disk rather than merely cached for later writes , writing the data to the faster ZIL storage then later flushing it out to the regular disks greatly reduces latency and improves performance.
Synchronous workloads like databases will profit from a ZIL alone. Regular asynchronous writes such as copying files will not use the ZIL at all. Unlike a traditional file system, ZFS writes a different block rather than overwriting the old data in place.
When completing this write the metadata updates to point to the new location. When a shorn write a system crash or power loss in the middle of writing a file occurs, the entire original contents of the file are still available and ZFS discards the incomplete write. This also means that ZFS does not require a fsck 8 after an unexpected shutdown.
Dataset is the generic term for a ZFS file system, volume, snapshot or clone. The root of the pool is a dataset as well. Child datasets have hierarchical names like directories.
This grandchild dataset will inherit properties from the parent and grandparent. Set properties on a child to override the defaults inherited from the parent and grandparent. Administration of datasets and their children can be delegated.
A ZFS dataset is most often used as a file system. Like most other file systems, a ZFS file system mounts somewhere in the systems directory hierarchy and contains files and directories of its own with permissions, flags, and other metadata. ZFS can also create volumes, which appear as disk devices. Volumes have a lot of the same features as datasets, including copy-on-write, snapshots, clones, and checksumming.
After taking a snapshot of a dataset, or a recursive snapshot of a parent dataset that will include all child datasets, new data goes to new blocks, but without reclaiming the old blocks as free space. The snapshot contains the original file system version and the live file system contains any changes made since taking the snapshot using no other space.
New data written to the live file system uses new blocks to store this data. The snapshot will grow as the blocks are no longer used in the live file system, but in the snapshot alone. Mount these snapshots read-only allows recovering of previous file versions. A rollback of a live file system to a specific snapshot is possible, undoing any changes that took place after taking the snapshot. Each block in the pool has a reference counter which keeps track of the snapshots, clones, datasets, or volumes use that block.
As files and snapshots get deleted, the reference count decreases, reclaiming the free space when no longer referencing a block. Each snapshot can have holds with a unique name each. The release command removes the hold so the snapshot can deleted. Snapshots, cloning, and rolling back works on volumes, but independently mounting does not.
Cloning a snapshot is also possible. A clone is a writable version of a snapshot, allowing the file system to fork as a new dataset. As with a snapshot, a clone initially consumes no new space. As new data written to a clone uses new blocks, the size of the clone grows. When blocks are overwritten in the cloned file system or volume, the reference count on the previous block decreases. Removing the snapshot upon which a clone bases is impossible because the clone depends on it.
The snapshot is the parent, and the clone is the child. Clones can be promoted , reversing this dependency and making the clone the parent and the previous parent the child. This operation requires no new space. Since the amount of space used by the parent and child reverses, it may affect existing quotas and reservations. Every block is also checksummed. The checksum algorithm used is a per-dataset property, see set.
The checksum of each block is transparently validated when read, allowing ZFS to detect silent corruption. Triggering a validation of all checksums with scrub.
Checksum algorithms include:. Deactivating checksums is possible, but strongly discouraged. Each dataset has a compression property, which defaults to off. Set this property to an available compression algorithm. This causes compression of all new data written to the dataset. Beyond a reduction in space used, read and write throughput often increases because fewer blocks need reading or writing. In the future, the default compression algorithm will change to LZ4.
One of the main advantages of using GZIP is its configurable level of compression. When setting the compress property, the administrator can choose the level of compression, ranging from gzip1 , the lowest level of compression, to gzip9 , the highest level of compression. This gives the administrator control over how much CPU time to trade for saved disk space. This compression algorithm is useful when the dataset contains large blocks of zeros.
When set to a value greater than 1, the copies property instructs ZFS to maintain copies of each block in the file system or volume. Setting this property on important datasets provides added redundancy from which to recover a block that does not match its checksum.
In pools without redundancy, the copies feature is the single form of redundancy. The copies feature can recover from a single bad sector or other forms of minor corruption, but it does not protect the pool from the loss of an entire disk.
Checksums make it possible to detect duplicate blocks when writing data. With deduplication, the reference count of an existing, identical block increases, saving storage space. The table contains a list of unique checksums, the location of those blocks, and a reference count. When writing new data, ZFS calculates checksums and compares them to the list. When finding a match it uses the existing block. Using the SHA checksum algorithm with deduplication provides a secure cryptographic hash.
Deduplication is tunable. If dedup is on , then a matching checksum means that the data is identical. Setting dedup to verify , ZFS performs a byte-for-byte check on the data ensuring they are actually identical. If the data is not identical, ZFS will note the hash collision and store the two blocks separately. As the DDT must store the hash of each unique block, it consumes a large amount of memory.
A general rule of thumb is GB of ram per 1 TB of deduplicated data. In situations not practical to have enough RAM to keep the entire DDT in memory, performance will suffer greatly as the DDT must read from disk before writing each new block. Consider using compression instead, which often provides nearly as much space savings without the increased memory.
Instead of a consistency check like fsck 8 , ZFS has scrub. A periodic check of all the data stored on the pool ensures the recovery of any corrupted blocks before needing them. A scrub is not required after an unclean shutdown, but good practice is at least once every three months.
ZFS verifies the checksum of each block during normal use, but a scrub makes certain to check even infrequently used blocks for silent corruption. ZFS improves data security in archival storage situations. Adjust the relative priority of scrub with vfs. ZFS provides fast and accurate dataset, user, and group space accounting as well as quotas and space reservations.
This gives the administrator fine grained control over space allocation and allows reserving space for critical file systems. ZFS supports different types of quotas: the dataset quota, the reference quota refquota , the user quota , and the group quota.
Quotas limit the total size of a dataset and its descendants, including snapshots of the dataset, child datasets, and the snapshots of those datasets. A reference quota limits the amount of space a dataset can consume by enforcing a hard limit. This hard limit includes space referenced by the dataset alone and does not include space used by descendants, such as file systems or snapshots.
The reservation property makes it possible to guarantee an amount of space for a specific dataset and its descendants.
Unlike a regular refreservation , space used by snapshots and descendants is not counted against the reservation. Descendants of the main data set are not counted in the refreservation amount and so do not encroach on the space set. Reservations of any sort are useful in situations such as planning and testing the suitability of disk space allocation in a new system, or ensuring that enough space is available on file systems for audio logs or system recovery procedures and files.
The refreservation property makes it possible to guarantee an amount of space for the use of a specific dataset excluding its descendants. In contrast to a regular reservation , space used by snapshots and descendant datasets is not counted against the reservation. When replacing a failed disk, ZFS must fill the new disk with the lost data.
Resilvering is the process of using the parity information distributed across the remaining drives to calculate and write the missing data to the new drive. A pool or vdev in the Online state has its member devices connected and fully operational.
Individual devices in the Online state are functioning. The administrator puts individual devices in an Offline state if enough redundancy exists to avoid putting the pool or vdev into a Faulted state.
An administrator may choose to offline a disk in preparation for replacing it, or to make it easier to identify. A pool or vdev in the Degraded state has one or more disks that disappeared or failed. Skip to main content. Radar Now, next, and beyond: Tracking need-to-know trends at the intersection of business and technology.
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