I am currently applying the finishing touches to my unRAID - but...

 

 

How is it exactly with the cache drive and power failure, does it act like a big bunch of RAM that looses memory when the power goes off - or does it just stay on the cache drive before being moved up to the real RAID next time it's powered on?

 

 

How about when my 500GB cache disc is full, does it automatically start moving data to the RAID and can I continue writing to the server s it moves data?

How is it exactly with the cache drive and power failure?

 

The cache drive is a physical disk (hard drive), not volatile memory like RAM. If you power off the computer (or lose power), whatever is on the cache drive will still be there when you turn the computer on again (just like any other hard drive).

 

Any data put on the cache drive will stay there until the mover script moves it off the cache drive onto one of your data drives. The mover script with default settings runs every night at 3:40am. You can change the time of the mover to be less or more often.

 

Your data drives are protected by your parity drive. If something goes bad with a data drive, you can replace it & the parity drive will restore your information. The cache drive does not have the protection of the parity drive. If the cache drive dies, it takes all your info that was stored on the cache drive with it.

 

More info on this can be found here: http://lime-technology.com/wiki/index.php/Cache_disk

 

How about when my 500GB cache disc is full, does it automatically start moving data to the RAID and can I continue writing to the server s it moves data?

 

From the bottom of the page link posted above:

Amount of data

The final consideration in choosing a cache drive is to think about the amount of data you expect to pass through it. If you write ~10 GBs per day, then any drive 10 GB or larger will do (a 30 GB SSD may be a good fit in this case). If you write 100 GB in one day every few weeks, then you will want a cache drive that is larger than 100 GB. If you attempt a data transfer that is larger than the size of your cache drive, the transfer will fail.

 

Also another link mentioning filling up your drives: http://lime-technology.com/wiki/index.php/Improving_unRAID_Performance#Avoid_filling_drives_.3E99.25

 

Avoid filling drives >99%

All filesystems can run into fragmentation and resulting performance problems when drives fill all the way up. With ReiserFS in unRAID, it can result in extremely slow write speeds and/or 10 to 30 second pauses where the drive and network share becomes unavailable (and can cause a windows machine trying to write a file to become somewhat unresponsive during that period). These pauses are believed to be the kernel searching the filesystem tree for free blocks or perhaps it is the filesystem adding area to the superblock (Reference). Depending on sizes of the files stored, it it proposed to stay below about 95 to 98% on each drive.

I think he answered your questions but I just wanted to add. A power failure should not result in your server getting shut down. Get a UPS, you will need to parity sync and will have errors every time the server improperly shuts down. It should never happen and can be avoided with a ~$100 device.

Hello, I can't see a response to the earlier question relating to - How about when my 500GB cache disc is full, does it automatically start moving data to the RAID and can I continue writing to the server s it moves data?

 

I would really appreciate a response as I have decent cache drive, and will have moves scheduled daily (hoping to avoid hourly), but worried what happens if the cache drive is maxed out, will drive stop accepting data, or will Unraid realize and start moving data from the cache to the parity/HDD's (I'm using UnRaid 6.1.8 btw)

Hello, I can't see a response to the earlier question relating to - How about when my 500GB cache disc is full, does it automatically start moving data to the RAID and can I continue writing to the server s it moves data?

 

I would really appreciate a response as I have decent cache drive, and will have moves scheduled daily (hoping to avoid hourly), but worried what happens if the cache drive is maxed out, will drive stop accepting data, or will Unraid realize and start moving data from the cache to the parity/HDD's (I'm using UnRaid 6.1.8 btw)

Depends. If you're writing to a share that utilizes the cache (but not set to cache only) then it will write directly to the array when the cache drive is full. Essentially bypassing it.

 

If it is a cache only share, I'm assuming it would refuse the write operation and give an error

Hello, I can't see a response to the earlier question relating to - How about when my 500GB cache disc is full, does it automatically start moving data to the RAID and can I continue writing to the server s it moves data?

 

I would really appreciate a response as I have decent cache drive, and will have moves scheduled daily (hoping to avoid hourly), but worried what happens if the cache drive is maxed out, will drive stop accepting data, or will Unraid realize and start moving data from the cache to the parity/HDD's (I'm using UnRaid 6.1.8 btw)

Depends. If you're writing to a share that utilizes the cache (but not set to cache only) then it will write directly to the array when the cache drive is full. Essentially bypassing it.

 

If it is a cache only share, I'm assuming it would refuse the write operation and give an error

Minimum free space needs to be set correctly for the intended usage.

Hello, I can't see a response to the earlier question relating to - How about when my 500GB cache disc is full, does it automatically start moving data to the RAID and can I continue writing to the server s it moves data?

 

I would really appreciate a response as I have decent cache drive, and will have moves scheduled daily (hoping to avoid hourly), but worried what happens if the cache drive is maxed out, will drive stop accepting data, or will Unraid realize and start moving data from the cache to the parity/HDD's (I'm using UnRaid 6.1.8 btw)

Depends. If you're writing to a share that utilizes the cache (but not set to cache only) then it will write directly to the array when the cache drive is full. Essentially bypassing it.

 

If it is a cache only share, I'm assuming it would refuse the write operation and give an error

Minimum free space needs to be set correctly for the intended usage.

For more details about share settings, see the help on the share settings page (toggle the Help button).

 

Here is an explanation of minimum free I posted some time ago.

Earlier comment from aptalca "Depends. If you're writing to a share that utilizes the cache (but not set to cache only) then it will write directly to the array when the cache drive is full. Essentially bypassing it"

 

Nice idea aptalca, I didn't realise i could enable cache, but not set to cache only, so UnRaid could bypass the cache if cache is full, nice work around.