Beginner questions.

[taichan]

Currently I'm looking at migrating away from a freenas 8 (Love the speed don't like the inablity to add extra drives.) box for my storage and have a few questions.

 

First question is cache drive.

 

I'm thinking of getting a 80-120GB SSD to do this but I read that if you copy more to it then avaible it fails. Does that mean if I get a 80GB SSD and try an copy 100GB folder it will fail? If so does that mean I should wait till after I transfered all my files before implimented the cache drive?

 

Also how much does the read/write speed of the cache drive matter?

 

As for parity drive. Would a 3tb 7200RPM drive be best for this? I plan on using 2tb WD Green (4x Ears and 5x earx and one eads)

 

Also should I stick to just Advanced formatted drives? Or is mix and matching not an issue?

 

Also if anyone has any experence with sickbeard/sabnzbd+ how well does this work? Its been amazing on my freenas box and I'm scared to have it working subpar.

[dgaschk]

Copies are done file by file. The files will be written to the cache drive until it is below the min free space setting. Then files will go straight to the array. If a file that is larger then the actual minimum free space fills the cache drive then the copy will fail for that file and all subsequent files. Add the cache drive after the array is full.

[chickensoup]

Copies are done file by file. The files will be written to the cache drive until it is below the min free space setting. Then files will go straight to the array. If a file that is larger then the actual minimum free space fills the cache drive then the copy will fail for that file and all subsequent files. Add the cache drive after the array is full.

 

+1

 

I have a 150GB cache drive and occasionally I need to copy more than this which can be annoying; the workaround is to copy it directly to the disk share (e.g. \\tower\disk7) so it doesn't use the cache drive. Additionally I have my cached drive share mapped to a drive (W:\ presently) so in Windows 7 I can see how full it is and run the mover manually if needed.

 

Cache drives make a noticable difference, particularly to writes. I've read that a faster parity drive can help with speeding up parity checks but I'm not 100% sure about this. unRAID handles all the formatting for you so don't worry about pre-formatting unless you want to minimise downtime.

[RackIt]

Reading wikipedia in regards raid4 (which is close to what unraid is), the parity drive seems to be the bottleneck.

 

So unraid is slow on writes and suffers greatly on multiple writes to multiple drives.  But I see unraid as a particular type of tool for a particular type of job; depending on your priorities.

 

If you want speed then use raid10, and I do already for some servers that need that speed.

 

Now, I also want an economical mass storage device for large files with some data protection and which are read more than written; aka multimedia files and image backups of network computers.

 

I couple unraid with CrashPlan and have a complete backup strategy; always having 3 copies of my data, one being off-site.

 

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With all that said, I'm setting up a separate unraid server to store my image backups.  Speed is a bit more important in this case.  So my intention is to create a 'hybrid' unraid and raid server.  Simply, I will create a cache drive out of 3 drives striped in order to boost write speeds and speedup backups.  The cache drive array will be large enough to handle a days worth of backups.

 

This is I get the speed I need each day and the benefits of unraid on day+1.

[S80_UK]

Reading wikipedia in regards raid4 (which is close to what unraid is), the parity drive seems to be the bottleneck.

 

So unraid is slow on writes and suffers greatly on multiple writes to multiple drives.  But I see unraid as a particular type of tool for a particular type of job; depending on your priorities.

 

To expand on that a little...

 

If you only have one device sending data to one share on one disk drive in the array, then the parity drive is not a bottleneck.  For each write to the array the data disk and the parity disk must both be read and written to once - so two operations each.  In that case the parity drive brings no great benefit by being faster than the data drive.

 

However, if you have multiple writes to the array happening to different disk drives in the array, then the parity drive speed has more of an influence since it is doing twice the work of each of the other drives.

 

The parity drive is not used when reading data except when there is a failed read from a data drive.

 

Ultimately it depends on the usage of the array - my parity drive is the same type as my data drives since it would not benefit my use of the server to have a faster one.