2020-02-07 12:32:09 +00:00
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# What is SPDK {#about}
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2017-12-26 20:22:55 +00:00
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The Storage Performance Development Kit (SPDK) provides a set of tools and
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libraries for writing high performance, scalable, user-mode storage
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applications. It achieves high performance through the use of a number of key
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techniques:
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* Moving all of the necessary drivers into userspace, which avoids syscalls
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and enables zero-copy access from the application.
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* Polling hardware for completions instead of relying on interrupts, which
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lowers both total latency and latency variance.
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* Avoiding all locks in the I/O path, instead relying on message passing.
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The bedrock of SPDK is a user space, polled-mode, asynchronous, lockless
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[NVMe](http://www.nvmexpress.org) driver. This provides zero-copy, highly
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parallel access directly to an SSD from a user space application. The driver is
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written as a C library with a single public header. See @ref nvme for more
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details.
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SPDK further provides a full block stack as a user space library that performs
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many of the same operations as a block stack in an operating system. This
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includes unifying the interface between disparate storage devices, queueing to
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handle conditions such as out of memory or I/O hangs, and logical volume
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management. See @ref bdev for more information.
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Finally, SPDK provides
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[NVMe-oF](http://www.nvmexpress.org/nvm-express-over-fabrics-specification-released),
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[iSCSI](https://en.wikipedia.org/wiki/ISCSI), and
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[vhost](http://blog.vmsplice.net/2011/09/qemu-internals-vhost-architecture.html)
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servers built on top of these components that are capable of serving disks over
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the network or to other processes. The standard Linux kernel initiators for
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NVMe-oF and iSCSI interoperate with these targets, as well as QEMU with vhost.
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These servers can be up to an order of magnitude more CPU efficient than other
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implementations. These targets can be used as examples of how to implement a
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high performance storage target, or used as the basis for production
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deployments.
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