1# What is SPDK {#about} 2 3The Storage Performance Development Kit (SPDK) provides a set of tools and 4libraries for writing high performance, scalable, user-mode storage 5applications. It achieves high performance through the use of a number of key 6techniques: 7 8* Moving all of the necessary drivers into userspace, which avoids syscalls 9 and enables zero-copy access from the application. 10* Polling hardware for completions instead of relying on interrupts, which 11 lowers both total latency and latency variance. 12* Avoiding all locks in the I/O path, instead relying on message passing. 13 14The bedrock of SPDK is a user space, polled-mode, asynchronous, lockless 15[NVMe](http://www.nvmexpress.org) driver. This provides zero-copy, highly 16parallel access directly to an SSD from a user space application. The driver is 17written as a C library with a single public header. See @ref nvme for more 18details. 19 20SPDK further provides a full block stack as a user space library that performs 21many of the same operations as a block stack in an operating system. This 22includes unifying the interface between disparate storage devices, queueing to 23handle conditions such as out of memory or I/O hangs, and logical volume 24management. See @ref bdev for more information. 25 26Finally, SPDK provides 27[NVMe-oF](http://www.nvmexpress.org/nvm-express-over-fabrics-specification-released), 28[iSCSI](https://en.wikipedia.org/wiki/ISCSI), and 29[vhost](http://blog.vmsplice.net/2011/09/qemu-internals-vhost-architecture.html) 30servers built on top of these components that are capable of serving disks over 31the network or to other processes. The standard Linux kernel initiators for 32NVMe-oF and iSCSI interoperate with these targets, as well as QEMU with vhost. 33These servers can be up to an order of magnitude more CPU efficient than other 34implementations. These targets can be used as examples of how to implement a 35high performance storage target, or used as the basis for production 36deployments. 37