In this test we are going to compare the input/output operations per second (IOps) between several hard drives we have by hand: Two enterprise 15000 rpm SAS (Serial Attached SCSI) hard drives, three high performance desktop 7200 rpm SATA drives, two low end desktop SATA drives and an enterprise SATA solid state drive.
To go directly to the comparison chart, click here.
Comparing hard drives is not only important in how many MB/s they are capable to transfer, it is important too to know how many IOps they are able to handle, that is, how many times per second they are able to read or write data in a given time. The IOps is a very important parameter in machines that handle lots of requests, e. g. computers running a database, which typically read and write a huge amount of small packets of data in a short amount of time.
With an every day example would be possible to easily understand the importance of IOps. Think in that you are going to copy a 2 GB AVI movie and then you are going to copy a 2 GB folder of pictures. The movie will copy at maximum speed, for say 100 MB/s and will take 20.5 seconds. The pictures will copy at 12.5 MB/s and will take almost 3 minutes. You can try this at home with similar files and you will see the huge difference among copying one thing and the other.
¿What is the difference in the example above if both are the same size? In simple (and coarse) terms, to copy the movie the hard disk head only needs to read the file position and then copy its content, only two operation are needed. To copy the pictures, the hard drive head needs to read the position of every single picture and copy its content, one by one; if each picture size is about 1.5 MB, there will be by 1500 pictures, that means by 3000 operations to copy all the pictures. In each operation the head takes a certain amount of time to finish the task and that causes a drop in the read or write speed of the disk.
With the developing of faster,bigger and reliable non-volatile memory chips (that doesn’t loose its content after cutting the power), new storages devices appeared in the market using the interface of the standard hard drives but instead of platters they used memory chips. Called Solid Stated Drives, a couple of years ago they had sky level prices (several thousands of dollars) but speeds that surpassed by far their mechanical counterparts produced increased sales and ultimately prices decreased with time.
The first models had problems with lifetime of memory chip sectors, that had a limited amount of read/write cycles, but nowdays internal SSD controllers have write leveling algorithms that keeps sector usage levered across the chips, equaling or surpasing MTBFs of disk drives. Additionally prices are getting lower and speeds keep increasing in each new model.
SSDs surpasses their disk counterparts in transfer rate (MB/s) twofold or more, however, the IOPS results are even more astonishing. In order to have concrete numbers of how many IOps a SSD is capable compared to a disk drive, we conducted a test using IOmeter usig a configuration profile posted in the Communiti forums of VMWare (http://communities.vmware.com/thread/73745), so results could be comparable with others.
The test simulatd a real life access to a database, with a transfer request size of 8 kB, 35/65% of random/sequential distribution; 65%/35% of read/write distribution and 64 outstanding IOps. The test ran for 5 minutes and was repeated 6 times per disk. The chart reports the mean and the standard error of the mean for each disk.
Additionally, the test were conducted over the last 10% of each drive because it is the slowest area in the disks, that means that it is a limiting factor of performance hence a representative (an more real) parameter of the behavior of the disks in a critical condition, that is, with the drives almost full.
Drives to test:
Seagate Cheetah 15k.5 ST373455SS, SAS 3Gb/s, 15000 rpm, 16 MB cache, 74 GB.
2. Fujitsu MAX3147RC, SAS 3Gb/s, 15000 rpm, 16 MB cache, 146 GB.
3. Seagate Cheetah 10T ST3300555SS, SAS 3Gb/s, 15000 rpm, 16 MB cache, 300 GB.
4. Seagate Barracuda ES.2 ST31000640SS, SATA 3 Gb/s, 7200 rpm, 16 MB cache, 1TB.
5. Seagate Barracuda ES.2 ST3500320NS, SATA 3Gb/s, 7200 rpm, 32MB cache, 500GB.
6. Seagate Barracuda 7200.12 ST31000528AS, SATA 3Gb/s, 7200 rpm, 32MB cache, 1TB.
7. Seagate Barracuda LP ST32000542AS, SATA 3Gb/s, 5900 rpm, 32MB cache, 2TB.
8. Hitachi Deskstar 5K1000 HDS5C1010CLA382, SATA 3 Gb/s, 5600 rpm, 8 MB cache, 1 TB.
9. SuperTalent Technology TeraDrive CT FTM12CT25H , SATA 3Gb/s, SSD, 120G.
The three first are enterprise SAS disk drides, fourth and fifth are SATA enterprise disk drives, sixth es a desktop performance SATA disk drive, seventh and eighth are home desktop disk drives and the last is an entrerprise Solid State Drive.
-2 x Processor Intel® Xeon E5620 ; 2,40 GHz, 12 MB cache, 1333FSB, Intel® HyperThreading technology, Intel® Turbo Boost technology.
-24 GB RAM DDR3 1333MHz ECC, (4GB x 6), triple channel config.
-SSD (Solid State Drive), 80 GB Intel X25M SSDSA2M080G2GC for the Operating System.
-SAS/SATA 6Gb/s controller, PCI-E 2.0 x8, HighPoint RocketRaid 2720, 8 ports.
-Video card NVidia GeForce 7300 GT.
-Mother board Supermicro with Chipset dual Intel® 5520, 36 líneas PCI-E 2.0 cada uno (72 total), 6.40 GT/s cada uno.
-2 x Gigabit Intel® 82574L LAN.
-Chasis 4U tower/rack muontable, high efficiency 1400W PSU.
-Windows 7 Ultimate de 64bit.
Well, lets the data chart talks by itself:
The difference between disk drives and the SSD was so big that I put labels in th chart to improve readiness.
Despite this is not a rigorous statistical test, it is enough to illustrate that differences are abysmal. The SSD is 18.5 to 21.6 time faster than a 15000 rpm SAS disk drive, but both have similar prices. Just imagine a RAID with this SSDs!
The big difference in IOps between drives is because the SSD controller needs very few time to locate a memory address in the chip, so while the hard drive head executes an operation the SSD executes 20 operations, that is, the disk head needs to fly over the disk until right position but the SSD simply locates electronically a row and a column to address the memory chip, a much faster operation.
This technology is in active development so we can expect a increase of perfromance of SSDs in the years coming, particularly because the interface bandwidth is increasing too. We already have SAS/SATA of 6 Gb/s and the 9 Gb/s is coming; plenty of transfer rate room.
We also need to wait what is the answer of hard drive manufacturers. The started with hybrid hard drives, but such a big differences and prices of SSDs falling is difficult to think that disk drives are going to keep the lead in the market for long time.
As a tip, all of our new workstations for renting are being produced using the SSD of this test as an operating system drive, so Windows and applications response times improved notably. We also have a customer whit a productions database implemented over 3 RAID1 of SSDs, running successfully and beating their previous SAS 15k system.
Stat tuned for more tests!