Hard drives thrashing while watching a movie

[Jello]

Title says it all...

I built a 4k movie server, with 8 X 8TB WD Reds and it runs OK except for one problem. Sometimes while watching a movie I can hear the hard drives thrashing, but the movie doesn't skip a beat...it plays flawlessly. I did a long smart test and everything was good. I can FTP into the box and transfer at about 700 MB/s , so I am assuming that I don't have a drive going bad. When I am transferring movies over to the box, everything sounds normal. I have it setup as raidz1 (just so I can sleep at night, not a big deal if I lost everything)
I did test the ram and it passed, the only issue being that 32 gigs isn't a supported config with this brand of memory according to the MB manufacturer. 16 gigs is so I could just take out one memory module and see what happens, but if I am just playing a movie, isn't Freenas just streaming from the hard drives?

tl;dr Can a ram issue affect a slow transfer where a faster transfer of 700 MB/s works flawlessly?

Thanks for your input. System specs below.

Edit - pool is 33% full
Edit #2 - After watching the movie I have transferred it back to my computer and did a bit by bit comparison and it is identical ... no errors in file
Edit #3 - Only happens for about 2 minutes.

 

[garm]

When a hard disk reads or writes it moves the arm. ZFS will write in data in chunks and a benefit of this is that the arm motion is somewhat reduced by it. When you read a file, the arm has to go to what ever spot the block happens to be at. When you “just stream” a file the arm has to fly all over the place and it it’s really fragmented that will be audible. Especially if you tax the throughout by reading a large file at high speed.

To monitor your drives health and ensure the health of the data in the pool you need to set up scheduled S.M.A.R.T tests, both long and short, and scrubs. Those tests should not only be run when an issue is suspected.

 

[Jello]

When you “just stream” a file the arm has to fly all over the place and it it’s really fragmented that will be audible. Especially if you tax the throughout by reading a large file at high speed.

Thanks for your reply. I checked for fragmentation and it is at 0% . When transferring at high speed there is no issue, only while streaming and only for about 2 minutes.

Edit - File fragmentation is not shown, just free space fragment at 0%. One would think with the pool at about 33% and has never been higher all files would get written to sequential blocks and there would be no file fragments, but I have deleted some stuff so maybe that is the issue. But what doesn't make sense is if I can transfer that file back to my other computer at ~700MB/s, why streaming at slow speed would cause all the noise.

 

[Chris Moore]

What doesn't make sense is why you are worried about it.

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