IOPS

IOPS (Input/Output Operations Per Second, pronounced eye-ops) is a commonly misused and misunderstood performance measurement used to characterize computer storage devices like hard disk drives (HDD), solid state drives (SSD), and storage area networks (SAN). Frequently mischaracterized as a 'benchmark', IOPS numbers published by storage device manufacturers do not relate to real-world application performance.

To meaningfully describe the performance characteristics of any storage device, it is necessary to specify a minimum of three metrics simultaneously, IOPS, response time, and (application) workload. Absent simultaneous specifications or response-time and workload, IOPS are essentially meaningless. In isolation, IOPS can be considered analogous to "revolutions per minute" of an automobile engine i.e. an engine capable of spinning at 10,000 RPMs with it's transmission in neutral does not convey anything of value, however an engine capable of developing specified torque and horsepower at a given number of RPMs fully describes the capabilities of the engine.

In 1999, recognizing the confusion created by industry benchmarketeering abuse of IOPS numbers following the release of IOmeter, the Storage Performance Council developed an industry-standard, peer-reviewed and audited benchmark that has been widely recognized as the only meaningful measurement of storage device IO performance; the SPC-1 benchmark suite. The SPC-1 requires storage vendors to fully characterize their products against a standardized workload closely modeled on 'real-world' applications, reporting both IOPS and response-times and with explicit prohibitions and safeguards against 'cheating' and 'benchmark specials'. As such, an SPC-1 benchmark result provides users with complete information about IOPS, response-times, sustainability of performance over time and data integrity checks. Moreover, SPC-1 audit rules require vendors to submit a complete bill-of-materials including pricing of all components used in the benchmark, to facilitate SPC-1 "Cost-per-IOPS" comparisons among vendor submissions.

Among the single-dimension IOPS tools created explicitly by and for benchmarketers, applications, such as Iometer (originally developed by Intel), as well as IOzone and FIO have frequently been used to grossly exaggerate IOPS. Notable examples include Sun (now Oracle) promoting it's F5100 Flash array purportedly capable of delivering "1 million IOPS in 1 RU" (Rack Unit). Subsequently tested on the SPC-1, the same storage device was only capable of delivering 30% of the IOmeter value on the SPC-1.

http://storagemojo.com/2009/10/12/1-million-iops-in-1-ru/ http://www.storageperformance.org/benchmark_results_files/SPC-1C/Oracle/C00010_Sun_F5100/c00010_Oracle_Sun-F5100-Flash_SPC1C_executive-summary.pdf

The specific number of IOPS possible in any system configuration will vary greatly, depending upon the variables the tester enters into the program, including the balance of read and write operations, the mix of sequential and random access patterns, the number of worker threads and queue depth, as well as the data block sizes. There are other factors which can also affect the IOPS results including the system setup, storage drivers, OS background operations, etc. Also, when testing SSDs in particular, there are preconditioning considerations that must be taken into account.

Performance characteristics

Random access compared to sequential access.

The most common performance characteristics measured are sequential and random operations. Sequential operations access locations on the storage device in a contiguous manner and are generally associated with large data transfer sizes, e.g., 128 KB. Random operations access locations on the storage device in a non-contiguous manner and are generally associated with small data transfer sizes, e.g., 4 KB.

The most common performance characteristics are as follows:

Measurement	Description
Total IOPS	Total number of I/O operations per second (when performing a mix of read and write tests)
Random Read IOPS	Average number of random read I/O operations per second
Random Write IOPS	Average number of random write I/O operations per second
Sequential Read IOPS	Average number of sequential read I/O operations per second
Sequential Write IOPS	Average number of sequential write I/O operations per second

For HDDs and similar electromechanical storage devices, the random IOPS numbers are primarily dependent upon the storage device's random seek time, whereas for SSDs and similar solid state storage devices, the random IOPS numbers are primarily dependent upon the storage device's internal controller and memory interface speeds. On both types of storage devices the sequential IOPS numbers (especially when using a large block size) typically indicate the maximum sustained bandwidth that the storage device can handle. Often sequential IOPS are reported as a simple MB/s number as follows:

$\text{IOPS} * \text{TransferSizeInBytes} = \text{BytesPerSec}$ (with the answer typically converted to MegabytesPerSec)

Some HDDs will improve in performance as the number of outstanding IO's (i.e. queue depth) increases. This is usually the result of more advanced controller logic on the drive performing command queuing and reordering commonly called either Tagged Command Queuing (TCQ) or Native Command Queuing (NCQ). Most commodity SATA drives either cannot do this, or their implementation is so poor that no performance benefit can be seen. Enterprise class SATA drives, such as the Western Digital Raptor and Seagate Barracuda NL will improve by nearly 100% with deep queues. High-end SCSI drives more commonly found in servers, generally show much greater improvement, with the Seagate Savvio exceeding 400 IOPS—more than doubling its performance.

While traditional HDDs have about the same IOPS for read and write operations, most NAND flash-based SSDs are much slower writing than reading due to the inability to rewrite directly into a previously written location forcing a procedure called garbage collection. This has caused hardware test sites to start to provide independently measured results when testing IOPS performance.

Newer flash SSD drives such as the Intel X25-E have much higher IOPS than traditional hard disk drives. In a test done by Xssist, using IOmeter, 4 KB random transfers, 70/30 read/write ratio, queue depth 4, the IOPS delivered by the Intel X25-E 64 GB G1 started around 10000 IOPs, and dropped sharply after 8 minutes to 4000 IOPS, and continued to decrease gradually for the next 42 minutes. IOPS vary between 3000 and 4000 from around the 50th minutes onwards for the rest of the 8+ hours test run. Even with the drop in random IOPS after the 50th minute, the X25-E still has much higher IOPS compared to traditional hard disk drives. Some SSDs, including the OCZ RevoDrive 3 x2 PCIe using the SandForce controller, have shown much higher sustained write performance that more closely matches the read speed.

Examples

Mechanical hard drives

Some commonly accepted averages for random IO operations, calculated as 1/(seek + latency) = IOPS:

Device	Type	IOPS	Interface	Notes
7,200 rpm SATA drives	HDD	~75-100 IOPS	SATA 3 Gbit/s
10,000 rpm SATA drives	HDD	~125-150 IOPS	SATA 3 Gbit/s
10,000 rpm SAS drives	HDD	~140 IOPS	SAS
15,000 rpm SAS drives	HDD	~175-210 IOPS	SAS

Solid-state devices

Device	Type	IOPS	Interface	Notes
Intel X25-M G2 (MLC)	SSD	~8,600 IOPS	SATA 3 Gbit/s	Intel's data sheet claims 6,600/8,600 IOPS (80 GB/160 GB version) and 35,000 IOPS for random 4 KB writes and reads, respectively.
Intel X25-E (SLC)	SSD	~5,000 IOPS	SATA 3 Gbit/s	Intel's data sheet claims 3,300 IOPS and 35,000 IOPS for writes and reads, respectively. 5,000 IOPS are measured for a mix. Intel X25-E G1 has around 3 times higher IOPS compared to the Intel X25-M G2.
G.Skill Phoenix Pro	SSD	~20,000 IOPS	SATA 3 Gbit/s	SandForce-1200 based SSD drives with enhanced firmware, states up to 50,000 IOPS, but benchmarking shows for this particular drive ~25,000 IOPS for random read and ~15,000 IOPS for random write.
OCZ Vertex 3	SSD	Up to 60,000 IOPS	SATA 6 Gbit/s	Random Write 4 KB (Aligned)
Corsair Force Series GT	SSD	Up to 85,000 IOPS	SATA 6 Gbit/s	240 GB Drive, 555 MB/s sequential read & 525 MB/s sequential write, Random Write 4 KB Test (Aligned)
Samsung SSD 850 PRO	SSD	100,000 read IOPS 90,000 write IOPS	SATA 6 Gbit/s	4 KB aligned random I/O at QD32 10,000 read IOPS, 36,000 write IOPS at QD1 550 MB/s sequential read, 520 MB/s sequential write on 256 GB and larger models 550 MB/s sequential read, 470 MB/s sequential write on 128 GB model
OCZ Vertex 4	SSD	Up to 120,000 IOPS	SATA 6 Gbit/s	256 GB Drive, 560 MB/s sequential read & 510 MB/s sequential write, Random Read 4 KB Test 90K IOPS, Random Write 4 KB Test 85K IOPS
(IBM) Texas Memory Systems RamSan-20	SSD	120,000+ Random Read/Write IOPS	PCIe	Includes RAM cache
Fusion-io ioDrive	SSD	140,000 Read IOPS, 135,000 Write IOPS	PCIe
Virident Systems tachIOn	SSD	320,000 sustained READ IOPS using 4KB blocks and 200,000 sustained WRITE IOPS using 4KB blocks	PCIe
OCZ RevoDrive 3 X2	SSD	200,000 Random Write 4K IOPS	PCIe
Fusion-io ioDrive Duo	SSD	250,000+ IOPS	PCIe
Violin Memory Violin 3200	SSD	250,000+ Random Read/Write IOPS	PCIe /FC/Infiniband/iSCSI	Flash Memory Array
WHIPTAIL, ACCELA	SSD	250,000/200,000+ Write/Read IOPS	Fibre Channel, iSCSI, Infiniband/SRP, NFS, CIFS	Flash Based Storage Array
DDRdrive X1,	SSD	300,000+ (512B Random Read IOPS) and 200,000+ (512B Random Write IOPS)	PCIe
SolidFire SF3010/SF6010	SSD	250,000 4KB Read/Write IOPS	iSCSI	Flash Based Storage Array (5RU)
Intel 750 1.2 TB	SSD	440,000 4KB Read IOPS 290,000 4KB Write IOPS	PCIe 3.0	One of the highest performing in its price class $899.99
(IBM) Texas Memory Systems RamSan-720 Appliance	FLASH/DRAM	500,000 Optimal Read, 250,000 Optimal Write 4KB IOPS	FC / InfiniBand
OCZ Single SuperScale Z-Drive R4 PCI-Express SSD	SSD	Up to 500,000 IOPS	PCIe
WHIPTAIL, INVICTA	SSD	650,000/550,000+ Read/Write IOPS	Fibre Channel, iSCSI, Infiniband/SRP, NFS	Flash Based Storage Array
Violin Memory Violin 6000	3RU Flash Memory Array	1,000,000+ Random Read/Write IOPS	/FC/Infiniband/10Gb(iSCSI)/ PCIe
(IBM) Texas Memory Systems RamSan-630 Appliance	Flash/DRAM	1,000,000+ 4KB Random Read/Write IOPS	FC / InfiniBand
IBM FlashSystem 840	Flash/DRAM	1,100,000+ 4KB Random Read/600,000 4KB Write IOPS	8G FC / 16G FC / 10G FCoE / InfiniBand	Modular 2U Storage Shelf - 4TB-48TB
Fusion-io ioDrive Octal (single PCI Express card)	SSD	1,180,000+ Random Read/Write IOPS	PCIe
OCZ 2x SuperScale Z-Drive R4 PCI-Express SSD	SSD	Up to 1,200,000 IOPS	PCIe
(IBM)Texas Memory Systems RamSan-70	Flash/DRAM	1,200,000 Random Read/Write IOPS	PCIe	Includes RAM cache
Kaminario K2	SSD	Up to 2,000,000 IOPS. 1,200,000 IOPS in SPC-1 benchmark simulating business applications	FC	MLC Flash
NetApp FAS6240 cluster	Flash/Disk	1,261,145 SPECsfs2008 nfsv3 IOPs using 1,440 15K disks, across 60 shelves, with virtual storage tiering.	NFS, CIFS, FC, FCoE, iSCSI	SPECsfs2008 is the latest version of the Standard Performance Evaluation Corporation benchmark suite measuring file server throughput and response time, providing a standardized method for comparing performance across different vendor platforms. http://www.spec.org/sfs2008.
Fusion-io ioDrive2	SSD	Up to 9,608,000 IOPS	PCIe	Only via demonstration so far.
E8 Storage	SSD	Up to 10 million IOPS	10-100Gb Ethernet	Rack scale flash appliance
EMC DSSD D5	Flash	Up to 10 million IOPS	PCIe Out of Box, up to 48 clients with high availability.	PCIe Rack Scale Flash Appliance

See also

• Instructions per second
• Performance per watt