question How many HDD's do you need in RAID 1 to be faster than an SSD on SATA 3 bottleneck?

[Shy Shy Tomato]

In read, of course.

[Enderman]

Random? Sequential? Queue depth?

You need to specify what kind of read.

Also, access latency will always be slower, no matter how many you have in raid.

[mariushm]

It depends on hard drive.

SATA 3 gives you 560 MB/s ... modern 4-8 TB drives can do 230-280 MB/s, so in theory a couple of them in RAID 1 will get close to 500 MB/s for some portion of the drives.

[WereCatf]

17 minutes ago, Shy Shy Tomato said:

How many HDD's do you need in RAID 1 to be faster than an SSD on SATA 3 bottleneck?

You can only achieve better read-speeds than with an SSD and even then, only for sequential data. For writes, you can't achieve that, no matter how many drives you add.

[Mira Yurizaki]

Even if we went to RAID 0, the HDDs would never be faster overall due to access times.

[Windows7ge]

I think you meant RAID0. Only some implementations of RAID1 work the way you're thinking while the rest don't read the data off the disks in stripes. That'd be a form of RAID1+0 where every disk contains a complete copy of the data but reads different chunks when requesting a file. You don't hear much popularly for this method.

 

As everyone else has said though there's a lot more to a drive than raw throughput. In terms of IOPS you would need one heck of a RAID array but for raw throughput 3~4 in RAID0 would be about equal.

[jjbeebe]

Its easy, just check out this link: https://www.thegeekstuff.com/2010/08/raid-levels-tutorial

[alex75871]

4x HDD in RAID 10 can probably saturate a SATA 3 bus in sequential reads. Still wouldn't come close in random IO though.

[Thirdgen89GTA]

Even you approach the the sequential throughput performance you'll never touch an SSD's ability to deal with Random IO, or latency.

 

SATA3 bottlenecks most things around 550MB/s.  A fast, 7200rpm consumer drive can reach past 200MB/s no problem these days.  So you only need about 3 drives in Raid 0.

 

When you uncork the SSD and give it a PCIe NVMe link that SSD can reach GIGABYTES per second.

 

Don't bother trying to replicate an SSD's IO performance with spinning rust, its not cost effective.  Tier your data.  Anything that NEEDS fast speeds should be on SSD.  Anything thats a streaming workload (such as a media server for home) can sit on spinning rust happily.