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We are currently using an HDD for our NetApp storage for our VMs. We're considering replacing them with SSDs, but many disk manufacturers have different performance. What range of latencies can we expect from SSDs versus HDDs? How much better are SSDs on average?
King David
Posted 2019-03-16T20:15:15.687
Reputation: 405
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The latencies of an SSD vary hugely, but in terms of IOPs (which us probably the term you want to google)you are looking at an increase in the order of 2-5 magnitudes. (Ie 100 iops for HDD, starting at more then 10000 + for an SSD).
Have a look at https://en.m.wikipedia.org/wiki/IOPS
SSDs are like a night and day difference. I would only use hdds for backups and unimportant archival data - like videos, music collections. A heavily swapping HDD can render a system unuseable - while it will just be a bit sluggish on SSD.
Speedwise SSDs are at least 5 times as fast in sequential reads and writes - which represents the closest benchmark
You did not ask, but SSD is also over 5 times as reliable as hdd (but unlike hdd more likely to fail completely and without warning - so RAID is still important)
davidgo
Posted 2019-03-16T20:15:15.687
Reputation: 49 152
If you reread my answer, you will see that I did. SSDs start at 5 times more throughput and go up from there – davidgo – 2019-03-17T06:20:11.263
another question please , lets say I have HHD disks , and by dmidecode , I get all disks details , can we according to the info from dmidecode find the iops? , if not maybe other linux command ? – King David – 2019-03-17T06:40:43.367
BTW - you said " latencies of an SSD vary hugely" but how it can be while iops is very good and latency is hudely? – King David – 2019-03-17T06:44:32.577
No. DMICode does not tell you about performance or provide particularly detailed info about disks. The only useful information it will provide is about the.motherboard/system model which can tell us something about the sata.controller and what types.of SSDs we can use. Smartctl and hdparm can provide the disk make and model and the iops can be lpoked up in its specs. – davidgo – 2019-03-17T06:45:58.403
By latencies I assume you mean IOPS (or some derivative thereof). These vary from 10k/sec to over 1m/sec – davidgo – 2019-03-17T06:47:59.257
ok so when I run Smartctl -a /dev/sdq , then what I need to capture from the output in order to find out the value about iops? – King David – 2019-03-17T06:51:48.367
You get the make and model and then find the specs for it from a datasheet, goigle or the seller. – davidgo – 2019-03-17T07:00:48.173
since the disks are connected to VM machine , we get "Device does not support Self Test logging" from Smartctl -a – King David – 2019-03-17T07:06:55.127
What does.hdparm -I /dev/sdq output? – davidgo – 2019-03-17T08:08:34.137