Today I was watching a movie and I decided to backup a couple I had laying around. When I started the backup the movie I was watching began to drop audio and frame stutter.

 

This got me wondering if I can watch two movies at the same time, on two different tv sets, without any issues?

 

Is there something wrong with my configuration settings that isn't allowing me to write and read at the same time?

Not necessarily. Are you writing to the same drive as reading? Do you have a cache disk? What are the hardware specifications? 

I can easily stream 6 movies at a time with no stuttering, even if they're all from the same disk.

 

However ... writing is an entirely different matter => every write to the protected array requires two reads and two writes ... a read from the drive being written to and the parity drive;  then a write to each.

 

That can easily cause stuttering if you're writing to the same disk you're streaming from.  Personally, I never write new movies to the array when it's in use for watching others.    I do all my backups on my PC, and then copy them to the array when it's not being used.

 

You can avoid any conflicts by simply installing a cache drive => then the writes will be to a different disk (the cache);  will be much faster (since they're not parity protected); and the actual movement of the data to the protected array will occur at times when the array isn't otherwise in use (assuming you have the mover scheduled to run at off-hours).

 

 

No cache disk. I have a parity drive and right now a single storage drive. I setup shares - video and various. I plan to add a disk or two when I get low on space, but the shares will remain the same. At some point I would think it would be hard to figure out what disk is being used to read, whereas the write disk should always be pretty easy to figure out since I'll only be adding one at a time. Takes me a bit to fill up 4TB of space.

 

I don't have specific hardware specs, but it's all newer stuff bought less than 3 months ago. Gigabit network, 4gb of ram, Intel Celeron G1610 Ivy Bridge 2.6GHz.

I can easily stream 6 movies at a time with no stuttering, even if they're all from the same disk.

 

However ... writing is an entirely different matter => every write to the protected array requires two reads and two writes ... a read from the drive being written to and the parity drive;  then a write to each.

 

That can easily cause stuttering if you're writing to the same disk you're streaming from.  Personally, I never write new movies to the array when it's in use for watching others.    I do all my backups on my PC, and then copy them to the array when it's not being used.

 

You can avoid any conflicts by simply installing a cache drive => then the writes will be to a different disk (the cache);  will be much faster (since they're not parity protected); and the actual movement of the data to the protected array will occur at times when the array isn't otherwise in use (assuming you have the mover scheduled to run at off-hours).

 

 

 

Can the cache disk be a smaller drive? Only large enough to hold enough data before transfer? Like a 1TB? 

 

 

Thanks for your input. There's some good info and some good options to pursue.

One other question:  Are you watching the movies by streaming the DVD VOB's, or is there transcoding needed to watch them (e.g. Plex) ??    This can have a major impact on how many you can watch at once.

 

The cache drive can be any size you want => obviously you want it to be large enough to hold as much as you're likely to write in a day.    Note that the free (Basic) version of UnRAID does not support a cache ... so you'll need to have at least a Plus license to do this.

 

One other question:  Are you watching the movies by streaming the DVD VOB's, or is there transcoding needed to watch them (e.g. Plex) ??    This can have a major impact on how many you can watch at once.

 

Streaming BD and DVD .ISO only. No trans-coding. All over a wired ethernet network.

The cache drive can be any size you want => obviously you want it to be large enough to hold as much as you're likely to write in a day.    Note that the free (Basic) version of UnRAID does not support a cache ... so you'll need to have at least a Plus license to do this.

 

Cool. I actually have two 8gb sandisk drives sitting here waiting for me to install the paid version of unraid on them. It's a chore to get these disks to act as a bootable drive. I wish unraid would update their install software, but I guess in all reality it isn't that hard to do the edit and make them bootable.

 

Cache drive sounds like a great idea. I'll order one when I order my next 4tb drive.

Streaming BluRay is clearly a bit more intensive than DVDs, but without any transcoding involved you should still be able to stream several at once with no problem.

 

I think you issue is purely due to the writes -- so a cache drive will resolve it.  Just be sure you schedule the mover at a time when you're not using the array.  I think it defaults to something like 3AM, but I'm not sure (I don't use a cache).

 

When you install the cache drive, be sure you change your share settings so they use the cache.

 

Streaming BluRay is clearly a bit more intensive than DVDs, but without any transcoding involved you should still be able to stream several at once with no problem.

 

I think you issue is purely due to the writes -- so a cache drive will resolve it.  Just be sure you schedule the mover at a time when you're not using the array.  I think it defaults to something like 3AM, but I'm not sure (I don't use a cache).

 

When you install the cache drive, be sure you change your share settings so they use the cache.

 

Will do. I'll read up as I'll need to set the auto transfer. I also need to setup an auto parity check and a couple of other things. Just been holding off until I pay for the license. Thanks again!

Streaming BluRay is clearly a bit more intensive than DVDs, but without any transcoding involved you should still be able to stream several at once with no problem.

It's not "a bit" more intensive, it's 5x the data rate. See my sig for tests I did a while back on multiple Blu-ray playback. That was with older drives, but I imagine it's really seek times that are the issue with multiple reads from the same drive.

Yes, BluRays are notably more intensive.    You should still be able to stream 3 at a time from a single disk with modern 1TB/platter drives with 64MB cache's and AHCI, although I'm not surprised you were limited in your tests using the 500MB/platter EARS and 250MB/platter EACS drives.  Those have a much lower data rate from the platter ... so you won't get anywhere near the IOPS that a modern WD Red or Seagate NAS unit will provide when reading relatively large blocks.

 

I've streamed 6 DVDs at once from the same drive with no problem -- and although the data rate isn't nearly as high as a couple of BluRays would be, the number of seeks (by far the slowest part of the disk I/O) is far higher than it would be for only 2 or 3 BluRays.

 

In any event, the question asked about streaming two movies at once -- and THAT should never be an issue, whether they're DVDs or BluRays, and whether or not they're on the same physical disk.   

 

Trying to do it while writing is, of course (as I outlined above), a different story 

Default cache mover schedule is 3:40am.

Default cache mover schedule is 3:40am.

 

What happens on the one day a month the auto parity check runs?

Default cache mover schedule is 3:40am.

 

What happens on the one day a month the auto parity check runs?

 

well, first off, a "monthly" parity check is not stock unraid. with that in mind, i bet a large portion of the user base have unmenu installed for this specific option.

 

the parcheck will continue during the mover execution, both will slightly slow down until mover is complete.

If you have both a cache drive and schedule automated parity checks, you may want to schedule the times so they're less likely to be running at the same time.  e.g. if you set the mover to run at 1:30AM and the automated checks to kick off at 3:30, it's very likely the mover will be done before the parity check kicks off.

 

Note that you do not have to automate the parity checks => you can simply run one once/month, once/quarter, etc. ... whatever you feel comfortable with.    The important thing is that you periodically check the array.

 

Now you've got me trying to figure this out.  I have a 1TB drive that I just did the parity deal and the format, but it is still empty.  I have the pro license, so can I just change this drive to a cache drive.  Other than just changing from a disk # to a cache drive, do I need to do anything else?  Thanx.

Now you've got me trying to figure this out.  I have a 1TB drive that I just did the parity deal and the format, but it is still empty.  I have the pro license, so can I just change this drive to a cache drive.  Other than just changing from a disk # to a cache drive, do I need to do anything else?  Thanx.

 

If it's currently a data disk (i.e. "disk #") you'll have to do a new configuration and assign it as a cache drive.  If it has data on it that you don't want to lose, be sure it' backed up before making the move.

 

OK, I now have a cache drive.  I'm have two shares Movies and TV.  Do I write direct to the cache, or just place it where it belongs under the TV or Movie and it automatically goes to cache until mover takes over?  If I write directly to the cache drive how does it know where to place the file?  Sorry for my ignorance, but this is absolutely all new to me.  Thanks Again.

For each of your shares you have to chose whether or not they're "cached".  If they're cached, then you just write to the share as normal => the actual write will be to the cache drive;  and later -- at "off hours"  (I believe it defaults to 3:40am) the system will move the data from the cache drive to your protected array.

 

This has two implications:

 

(1)  Writes are much faster, since you're writing at the speed of the cache drive;

 

and

 

(2)  The data is NOT fault-tolerant when you write it ... only after it's been moved to the protected array.

 

Whether it's on the cache drive or your array is basically transparent to you.  The cache drive simply gives you faster writes.    Personally, I ALWAYS want the data I've written to UnRAID to be fault-tolerant; so I do not have a cache.

 

Thanks, Gary.  I see that option for the cache drive now.  Currently, I can't write directly to the array, cause I gat a Posix error and it fails using MakeMKV, so I have to write to my SSD in my iMac and move it to the array.  So in all my brilliance, I figure maybe I can write to the cache and then copy to the array.  I gonna have to play with this for awhile.  Thanks Again.