Building a NAS that will be primarily used as a media server but will also be used to archive important, rarely accessed things like tax returns/scanned documents, etc.  Also considering ZFS RAIDz1 or RAIDz2 but that idea is losing traction and the unRAID is looking very attractive.

 

#1 - I just want to make sure that I understand the cache drive.  My understanding is that it handles all writes during the course of the day and then writes to the array (if that's even the proper terminology for unRAID) during a scheduled downtime.  So, if this is the case I could just pick up an inexpensive 60GB SSD for the cache drive and my GigE network would be the limiting factor for writes in my unRAID setup, correct?  I understand the possibilty of lost data if the SSD were to crash before the nightly write to the array.

 

#2 - I know that Green drives are OK for an unRAID setup, but how much lag for spin-up would I expect versus using some 7200rpm Seagates, Toshibas or WD Reds?  I know it's really a tiny issue but it's something that I find very aggravating when sorting through my media library.  I want to pull up the library and have the titles available as close to instantly as possible.  It would be worth investing a little amount of $$$ to make sure a 2 second or greater lag would not be there.

#1, you are correct.  but I would skip the SSD and get a fast spinner.  A modern fast spinner will still saturate your GigE and will not put you at risk of running out of room on the cache before the next MOVER event

 

#2 drive speed has no real impact on spin-up delay. Heck, if anything a slower drive might actually get to full speed faster since full speed is well ... slower ;-)  Beyond that, reading/writing directly to the array is only marginally impacted by spindle speed, but power and heat is highly impacted by spindle speed.  So that 2- second lag cannot be avoided, or even shortened much.

 

HOWEVER, there are software methods to help reduce / eliminate that lag.  Look into the Cache-Dirs add-on script.  In short, it stores your directory structure in memory for fast traversing.  However once you invoke a file, there will be a delay if that drive hasn't spun up. 

 

FYI, that delays is only the first time the drive spins up ... set your spin-down timer correctly and you won't have to worry about it again until you step away for X time vice having to deal with it in the middle of doing whatever you're doing.

#1, you are correct.  but I would skip the SSD and get a fast spinner.  A modern fast spinner will still saturate your GigE and will not put you at risk of running out of room on the cache before the next MOVER event

 

Cool, that would have been my next question, SSD vs. Disk based speed on a GigE network.

 

#2 drive speed has no real impact on spin-up delay. Heck, if anything a slower drive might actually get to full speed faster since full speed is well ... slower ;-)  Beyond that, reading/writing directly to the array is only marginally impacted by spindle speed, but power and heat is highly impacted by spindle speed.  So that 2- second lag cannot be avoided, or even shortened much.

 

HOWEVER, there are software methods to help reduce / eliminate that lag.  Look into the Cache-Dirs add-on script.  In short, it stores your directory structure in memory for fast traversing.  However once you invoke a file, there will be a delay if that drive hasn't spun up. 

 

FYI, that delays is only the first time the drive spins up ... set your spin-down timer correctly and you won't have to worry about it again until you step away for X time vice having to deal with it in the middle of doing whatever you're doing.

 

Not too worried about spindle speed.  I can't envision a scenario where 5400rpm vs. 7200rpm could be an issue.  I was just wondering how the head parking of the WD Green drives affects the drives ability to quickly spin-up and send information as it is requested by my media streamers.  I know that there's going to be some delay with ANY drive so the Cache-Dirs add-on script looks like something I'll dig into.  I'm fairly accustomed to a little lag after the movie has been chosen and I'm not bothered by it.  It's that 5 seconds when I click "My Media Library" before the album artwork/movie posters populate and I am sitting there wondering if there's a problem and I'm going to have to reboot everything  .

I hear ya on the delay.  I guess I just got used to it since it only occurs that first time I hit the server after a while.  As to head parking WD Greens ... well they all head park to some extend really, but you will not notice that at all if the spindle is at least already spinning.  That said, do check out the info in wdidle when it comes to some of the WD Greens.  I'm not sure if the new drives still need to have wdidle modified to prevent excessive load cycle counts (LCC), but you should be informed about the issue just in case.

Thanks for the tips on wdidle. 

 

I only have one 2TB Green that I was considering for use with unRAID.  I think I'll just skip them and go with a WD Red or different brand and relegate the 2TB Green to a USB enclosure for backing up critical data.

no no, do not write off WD Greens.  Plenty of folks use them here with great effect.  But some, I think only the EARS line, (again be informed, do the research), just need to have a setting tweaked to avoid a high LCC accumulation.

 

Fact is, there are so few drive vendors now, you can't really afford to write off WD so long as they are still making decent drives.