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How much faster is a server equipped with a SSD than a mechanical hard disk

2020-11-08 16:17:46 Zhang Yanfei Allen

I believe you all know that SSD (SSD) The advantage of this is that it is faster than the traditional mechanical hard disk (HDD) Be quick , So now more and more solid-state drives appear in online servers . But as a development that cares about performance numbers , I want to be more precise about carrying SSD The server is in IO The performance is better than that of carrying HDD How much faster , The order IO How much faster in the case of , Random IO How much faster under the circumstances ? Finally, I took time to do a performance test recently .

Test environment

I found two servers , The disks are all Raid array , They are carrying SSD and HDD, More detailed configuration is as follows :

  • HDD Real machine :
    • Raid The card model is PERC H730 Mini,1GB RAM cache
    • 4 block 500GB SSD Composed of raid5, Available capacity 1.3T
  • SSD Real machine :
    • Raid The card model is the same as above
    • 7 block 300G HDD The hard disk makes up Raid5, Available capacity 1.6T

Okay , The contestants are in position , Then select the pressure measuring tool fio. Designated ratio ( Pressure ) " ( measuring ) gauge ( ginseng ) be ( Count ) as follows :

  • IO engine : In order to put enough pressure on the hard disk , Choose asynchronous mode libaio
  • PageCache: In order to get closer to the performance of the disk itself , Turn on Direct Parameters bypass Linux System memory cache
  • Pressure test object : On the safe side , No naked device used , The files used
  • file size :100GB, Because of my Raid The card cache is 1G, The guarantee is much bigger than the cache
  • Scheduling strategy : Choose common noop

The contrast test officially began .

Sequential read PK

Let's start with a test under sequential access , Because in this environment, whether it's a mechanical hard disk , Or a solid-state drive , Performance will be optimal .IO Size from 512K Until 1M.

Let's take a look at the mechanical hard disk :

file

Under SSD : file

The data looks like , In order IO Under the circumstances , Actually, it carries HDD Server for IO Performance is not being carried ssd It's falling too much . This is because

  • The order IO Under the circumstances ,RAID The card has a high hit rate , Especially when it's set up RAID Prefetch
  • In its own order IO It's also the best state of mechanical disk work

therefore , Modern in the field of servers ,SSD It's just that there are more and more applications , But it doesn't replace HDD. One of the reasons is because of the order of the mechanical hard disks IO It's not slow , Plus Raid Blessing , So there's a big market share . After comparing the order IO, Let's compare another application scenario , Random IO.

Random reads PK

Remember the beginning fio In the pressure measurement parameters, we put Page Cache It's disabled , Plus the size of the test file is 100GB, This is much more than Raid The cache size of the card . So random based on this premise IO, All levels of cache are basically out of use ,IO Performance speed depends entirely on the hard disk itself .

stay 《 Mechanical hard disk random IO Slower than you think 》 in , We look at the random of mechanical hard disks IO It's really bad performance .

file

Let's look at carrying SSD Server for IO performance :

file

By contrast , Mechanical hard disk random IO It's not that slow , We choose the most recognized result of the above 4K IO size Look at .

  • From a bandwidth perspective , Only less than 1M The throughput of ,
  • From the perspective of delay , stay 4.4ms about

Let's look at the SSD 4K IO Size Next performance . And under the same conditions SSD Can have 32M.

  • From a bandwidth perspective , There are still 32M, Than HDD It can be dozens of times faster
  • From the perspective of delay , about 120us about . Than HDD, Namely 4400:120, It's also dozens of times higher

summary

In order IO Under the circumstances , Because there is Raid The blessing of card cache , be based on HDD Composed of Raid The array server is in IO The performance is not too bad . But in a random read scenario , Whether bandwidth or latency metrics ,SSD It's better than HDD More than ten times faster . So in the server application SSD, The main solution is random IO The problem of . So if you have too many Page Cache,Raid Card cache can't hold random IO request , Then please put HDD Replace it with SSD Well .


file


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