Cache Drive not faster

[Witty321]

I'm totally new to unRaid. I just built my server and installed a Samsung Evo850 250GB SSD as the cache drive and set shares to use the cache. I have a 3TB WD Red data disk and a 5TB Seagate as the Parity disk. I've started populating my server and am getting write speeds of 110MB/s without the cache and the same with. I thought the cache drive would make the writes much faster as it doesn't need to calculate parity until it runs the mover which is set to run every night at 4am. Am I doing something wrong or is 110MB/s the fastest i can get?

[Squid]

32 minutes ago, Witty321 said:

Am I doing something wrong or is 110MB/s the fastest i can get?

If you're copying files over the network and are on a 1Gbps network, then yes that is the fastest you'll get

 

With the massive speed increases in how unRaid can directly write to the array with faster drives, controllers, etc many people don't even bother using the cache drive for shares, and limit it to a so-called "Application" drive (ie: docker.img, appdata, downloads shares, etc)

 

But, either way you are always limited by your network speed when transferring files to unRaid over the network.

[trurl]

Do you have turbo write on? The speed you say you are getting without cache is faster than expected.

[pwm]

Just now, trurl said:

Do you have turbo write on? The speed you say you are getting without cache is faster than expected.

I have never tried an unRAID with only one data disk but remember that with just a single data disk the parity can be written directly without reading back any old content. So turbo write or not shouldn't matter.

[trurl]

8 minutes ago, pwm said:

I have never tried an unRAID with only one data disk but remember that with just a single data disk the parity can be written directly without reading back any old content. So turbo write or not shouldn't matter.

 

Yes, that makes sense. Parity is just a mirror of the single disk in that scenario.

 

WItty321, if you get additional data disks, you can expect the write speeds to drop considerably when not using cache. Even so, I don't cache writes to my user shares because I am not concerned with the write speed.

[Witty321]

35 minutes ago, trurl said:

Do you have turbo write on? The speed you say you are getting without cache is faster than expected.

 

What is turbo write? Is this a thing and if so what are the pros and cons of using it?

 

43 minutes ago, Squid said:

If you're copying files over the network and are on a 1Gbps network, then yes that is the fastest you'll get

 

With the massive speed increases in how unRaid can directly write to the array with faster drives, controllers, etc many people don't even bother using the cache drive for shares, and limit it to a so-called "Application" drive (ie: docker.img, appdata, downloads shares, etc)

 

But, either way you are always limited by your network speed when transferring files to unRaid over the network.

 

I didn't realy think about gigabit network speed...I now see that it equals about 125MB/s...so I really can't go any faster without upgrading my network hardware.

 

25 minutes ago, trurl said:

 

Yes, that makes sense. Parity is just a mirror of the single disk in that scenario.

 

WItty321, if you get additional data disks, you can expect the write speeds to drop considerably when not using cache. Even so, I don't cache writes to my user shares because I am not concerned with the write speed.

 

So as I populate my array with more disks the write speeds will slow down as the parity write gets more complicated? So then my cache drive should still write at aprox. 115MB/s and my array of data disk will slow as I add more drives to the array.

[Witty321]

40 minutes ago, pwm said:

I have never tried an unRAID with only one data disk but remember that with just a single data disk the parity can be written directly without reading back any old content. So turbo write or not shouldn't matter.

 

I'm going to be adding more drives to the array as I slowly empty my Windows Storage Spaces pool. As I transfer those files to my unRaid server I can start taking the drives from it and adding them to my array.  I currently have 6 - 3TB WD Red's in external enclosures hooked to my laptop via a USB hub (it's terrible) hence why I built the unRaid server. I just don't have enough empty disks to transfer it all in 1 go so it's 1 drive at a time. Also why I want to get the fasted write speeds as possible with my hardware as this is a slow but informative process. And my wife will be happy when all the cords are off the living room floor

[ken-ji]

I don't remember if the Windows Storage Spaces drive pools can be broken up into individual drives, but if yes:

You do have the option of installing the Unassigned Devices plugin

and attache one drive (or more is unRAID array space permits) directly to your unRAID box.

Then you use the plugin to mount the drives and use the builtin mc (midnight commander) console utility (or some docker like Krusader - which I never used) to copy the data from the USB enclosure to the unRAID array without going through the horribly slow network - with Turbo Mode turned on, youshould be able to copy at the 200MB/s speed if your drives are that fast)

Don't have a link/tutorial for you at this point as I know how to use mc like the back of my hand - but its not hard to work out.

[trurl]

1 hour ago, Witty321 said:

So as I populate my array with more disks the write speeds will slow down as the parity write gets more complicated?

 

Only 1 data disk is simpler and faster than more than one, but 2,3,4,... are all the same complication and same speed. There is no additional speed penalty for each additional disk.

 

1 hour ago, Witty321 said:

What is turbo write? Is this a thing and if so what are the pros and cons of using it?

 

The explanation of turbo vs "normal" parity updates is also a good place to learn about why parity updates don't get slower with each additional disk.

 

Here is a link:

 

https://lime-technology.com/forums/topic/50397-turbo-write/

 

And here is a link for how parity works, which shows that parity is the same calculation for any number of disks.

 

https://lime-technology.com/wiki/UnRAID_6/Overview#Parity-Protected_Array

 

Everything about how unRAID operates makes more sense if you understand parity.