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Input/output performance measurement
Input/output operations per second (IOPS, pronounced eye-ops) is an input/output performance measurement used to characterize computer storage devices like hard disk drives (HDD), solid state drives (SSD), and storage area networks (SAN). Like benchmarks, IOPS numbers published by storage device manufacturers do not directly relate to real-world application performance.[1][2]
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 of 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 its 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.
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.[1] 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.[3]
Performance characteristics[edit] 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 secondFor 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.[1] Often sequential IOPS are reported as a simple Megabytes per second number as follows:
(Then converted to MB/s.)
Some HDDs/SSDs will improve in performance as the number of outstanding IOs (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). Many consumer SATA HDDs either cannot do this, or their implementation is so poor that no performance benefit can be seen.[citation needed] Enterprise class SATA HDDs, such as the Western Digital Raptor and Seagate Barracuda NL will improve by nearly 100% with deep queues.[4] 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.[citation needed]
While traditional HDDs have about the same IOPS for read and write operations, many NAND flash-based SSDs and USB sticks are much slower writing than reading due to the inability to rewrite directly into a previously written location forcing a procedure called garbage collection.[5][6][7] This has caused hardware test sites to start to provide independently measured results when testing IOPS performance.
Flash SSDs, such as the Intel X25-E (released 2010), have much higher IOPS than traditional HDD. 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 approximately 50 minutes and onwards, for the rest of the 8+ hours the test ran.[8] 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.[9] For example, a typical operating system has many small files (such as DLLs ≤ 128 kB), so SSD is more suitable for system drive.[10]
Mechanical hard drives[edit]Block size used when testing significantly affects the number of IOPS performed by a given drive. See below for some typical performance figures:[11]
Does not appear Metric → IOPS IOPS MB/s IOPS IOPS MB/s Drive Block size → 4 KB 64 KB 64 KB 512 KB 512 KB large Type RPM Access type → random random random random random sequential SAS 15 K 188 – 203 175 – 192 11.2 – 12.3 115 – 135 58.9 – 68.9 91.5 – 126.3 FC 15 K 163 – 178 151 – 169 9.7 – 10.8 97 – 123 49.7 – 63.1 73.5 – 127.5 FC 10 K 142 – 151 130 – 143 8.3 – 9.2 80 – 104 40.9 – 53.1 58.1 – 107.2 SAS 10 K 142 – 151 130 – 143 8.3 – 9.2 80 – 104 40.9 – 53.1 58.1 – 107.2 SATA 7200 73 – 79 69 – 76 4.4 – 4.9 47 – 63 24.3 – 32.1 43.4 – 97.8 SATA 5400 57 55 3.5 44 22.6 Solid-state devices[edit] Device Type IOPS Interface Notes Intel X25-M G2 (MLC) SSD ~8,600 IOPS[12] SATA 3 Gbit/s Intel's data sheet[13] 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[14] SATA 3 Gbit/s Intel's data sheet[15] 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.[16] G.Skill Phoenix Pro SSD ~20,000 IOPS[17] 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.[17] Samsung SSD 850 PRO SSD Up to[neutrality is disputed] 100,000 read IOPS{{cite web}}: CS1 maint: archived copy as title (link){{cite web}}: CS1 maint: archived copy as title (link){{cite web}}: CS1 maint: archived copy as title (link)Samsung tests NVMe products with four workers at QD4
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