RAID 5 slowing down transfers?

agour · 29 Nov 2016 at 17:12

Hi all,

I put a RAID 5 in my PC (four 3TB drives), and notice that it has reaaally slow transfer speeds when compare to a normal drive.

USB 3 -> RAID = 11MB/s

USB 3 -> SSD = 55-70MB/s

USB 3 -> HDD = 55-70MB/s

I'm wondering... why? Is it due to the large capacity drives?

Cheers!

agour · 29 Nov 2016 at 17:20

BTW this is copying about 32GB of small files (every file is 20MB)

Also when I copy the files from RAID -> SDD, I get 70MB/s. Edit: this has now peaked to 230MB/s

skyripper · 29 Nov 2016 at 17:37

For every set of block of data you write to your drives, your motherboard has to calculate another block parity data and write that too.

And it spreads it around from drive to drive. So poor write performance is expected with Raid5. Normally the controller doesn't start writing the next set of blocks until all the previous set us all written, so caching and buffers become less efficient.

Steviepunk · 29 Nov 2016 at 17:40

Have a read here for general information on how RAID works and the performance implications, http://www.storagecraft.com/blog/raid-performance/

If you are just using RAID5 from your motherboard, then it will most likely be using your CPU to do the heavy lifting, so possible you're CPU will be a bottle neck in the process. Also, that artcile explains that a RAID5 array does a lot more when writing data as it has to perform data integrity checks as it is writing.

agour · 29 Nov 2016 at 18:54

That makes a lot of sense.. thanks guys! I've now delete the raid and gone back to normal HDD use.

ToTheMax · 30 Nov 2016 at 19:45

If you are looking for some resiliency I would recommend MS storage spaces, configure it like a raid 10 array (2 column mirror) and it's extremely fast. The only downside is you half your drive capacity but software raid 5 as you found isn't fit for purpose imo.

Liquidfox · 1 Dec 2016 at 22:19

RAID1 is more than enough for home use. It gives you some redundancy with none of the downsides associated with more complex RAID arrays.

Toxophilus · 5 Dec 2016 at 23:03

Liquidfox said:
RAID1 is more than enough for home use. It gives you some redundancy with none of the downsides associated with more complex RAID arrays.

I must agree RAID 1 for Home use is normally the way to go. Raid 5 is more for business redundancy when you want better availability. If you think times are slow with normal running if you need to rebuild a disk into the array it goes super slow then.