Dwaddle is spot on with "...it depends..."
There is another aspect to bring into the discussion about I/O Operations Per second (IOPSs) which is the average size in kbytes of the work being done. As Dwaddle mentioned, various types of hard disk drives (HDDs), Hybrid HDDs (HHDDs) and solid state devices (SSDs) will have different IOP capabilties however those metrics are tied to work being done of a given size. The smaller the IO size, the higher the IOP and lower the bandwidth or throughput numbers, likewise, the larger the IO size, higher bandwidth or throughput will be seen with lower IOPs. Also keep latency or response time in mind which for IOPs should be lower for interactive or transactional activity.
Even though some HDDs can do 210 or more IOPSs, those IOPs are of a small size say 4Kbytes to 8Kbytes (check with specific vendors spec sheets) however depending on how those HDDs are attached to your computer or server will make a different. In addition to the type and speed of the interconnect (USB 2.0/3.0, SAS 3G/6G, 1GbE iSCSI, Fibre Channel, SATA, etc) the type of adapter, controller or storage system will also help or in some cases hinder the native drive performance. Generaly the controller, adapter or storage system should be neutral or boost performance with caching and other techniques. However it is possible where a controller or adapter or storage system can be implemeneted in a manner where the full drive potential is not realized. Likewise there are controllers, adapters and storage systems that are actually starved by not having enough HDDs to service IO which also tend to be a sign of the need for SSD or faster drives.
Also as Dwaddle mentions, RAID configuration can make a big differences with RAID 0 (stripe) being the fastest for reads and writes however it also provides no protection, in fact it actually introduces the risk of a single drive failure taking the entire stripeset off line. As a result it is typically only used for static or read data that can be rapidly restored from another disk, tape or other means. RAID 1 (mirroring) gives both good read and write performance however it has the highest capacity space overhead of the RAID levels. RAID 10 (1+0) and (0+1) stripe & mirror/mirror & stripe provide a good balance of performance with protection where data are stripped and mirrored (or mirrored and stripped) however at the expense of extra storage capacity. RAID5 is stripe with rotating parity and is very popular for concurrent reads however imposes a write penalty (hence need for battery backed write cache in controller/adapter/storage system) due to parity calculation operations. RAID 6 is popular for using large capacity low cost drives using dual parity with stripe to protect against a double drive failure. Another popular RAID option is RAID 4 which is what NetApp uses as a variation for their default proteciton in addition to the RAID DP (Douple Parity).
Reads will typcially be faster than writes, hence a higher percentage of smaller reads should yield a higher IOP rate (guess what vendors like to show for benchmark numbers? ) and hopefully lower latency. Likewise for high bandwidth or throughout to to show large number of MBytes or GBytes per second, the game is to use very large IOs of 64K, 128K or bigger such as would be seen with backup/restore, streaming video/audio, bulk data movement and other sequential operations. Cache in the controller/adapter/storage system can help particular on reads however there can also be write benefits.
There is much more to the topic, however hopefully that gives you more to think about. If you are interested or want to know more, check out my blog http://storageioblog.com or main website http://storageio.com where you can find articles, tips, videos, podcast, reports and other related content. In addition, in my books Cloud and Virtual Data Storage Networking (CRC Press), The Green and Virtual Data Center (CRC Press) and Resilient Storage Networkss (Elseiver) I go into more discussion about IOPs, reads, writes, performance, workloads, benchmarking, storage systems and other related topics.
Cheers
gs
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