UnRaid Config Options

[jeffreywhunter]

I'm building an 18TB UnRaid with the following configuration:

http://my.jetscreenshot.com/12412/20150325-ofch-20kb

 

I have several spare systems I can use, but I'm going with the ASUS M5A97 since it has all 6 ports at 6Gb/s.  Assuming 12GB is more than enough anyway.  Although i do play to run PlexApp and perhaps some others.

 

I'm expanding SATA ports with the Supermicro AOC-SAS2LP-MV8 on PCI-E X16 Slot.  I have gigabit ethernet.

 

Given this config, I'm looking at a 750 GB SSD for the Cache Drive and 4 TB drive for Parity.

 

Here's my questions:

 

1. Will the difference of a 7200 RPM drive vs 5900 RPM drive make that big of a difference for the Parity drive?

2. Regarding Cache - better to have more space or speed?  For options I have 750 GB and 128 GB SSD's I could use for Cache.  Would 128GB SSD be enough of a cache?  Or should I go with a 2 TB 7200 RPM HDD (esp since a good 2 TB Drive should max ethernet)?

3. I'm assuming its better to use the Board SATA ports before I use the PCI-E Sata Card and that the smaller/slower drives are better on the PCI-E.

4. Given the speed of the parity drive is slower, better to put that on the PCI channel?

 

thanks in advance for your experience...

Jeff...

 

 

[garycase]

1. Will the difference of a 7200 RPM drive vs 5900 RPM drive make that big of a difference for the Parity drive?

 

Depends primarily on how you're using the array.  The more significant difference between the two speeds is that a 7200rpm unit will have faster access times.  If you're doing a lot of simultaneous writes from various clients (or multiple threads on the same client), then the faster seeks will speed up the overall average write times.  If you typically only have one client doing writes, then there's no notable advantage to the parity drive being a faster rpm unit than the data drives. 

 

Edit:  I just noted that all of your data drives are 7200rpm.  In this case, it would be beneficial if the parity drive was too => with the slower drive it's a bit of a bottleneck for your write speeds.

 

 

2. Regarding Cache - better to have more space or speed?  For options I have 750 GB and 128 GB SSD's I could use for Cache.  Would 128GB SSD be enough of a cache?  Or should I go with a 2 TB 7200 RPM HDD (esp since a good 2 TB Drive should max ethernet)?

 

Depends on several things:  (a)  If you're only using the cache drive as a true cache, then you're correct ... as long as it maxes the Ethernet connection, it doesn't make a lot of difference.    (b)  If you're using it as an application storage location, then the speed of an SSD will be beneficial for the local application.  ©  In any event, you want to be sure it's large enough to cache whatever you're likely to write in between Mover sessions.

 

 

3. I'm assuming its better to use the Board SATA ports before I use the PCI-E Sata Card and that the smaller/slower drives are better on the PCI-E.

 

The SAS2LP-MV8 has plenty of bandwidth to support the maximum transfer rates of all of your drives, so it really doesn't matter. 

 

 

4. Given the speed of the parity drive is slower, better to put that on the PCI channel?

 

I presume you mean the PCIe bus on the SAS2LP.  As I noted above, either way is fine, as all of your SATA ports, both motherboard and on the SAS2LP, support 6Gb/s operation.

 

 

[jeffreywhunter]

Hey Gary,

 

Excellent information, thanks for sharing.  The only remaining question is that I purposefully bought a larger drive (the 4TB) so that I could expand later.  Unfortunately, I didn't consider the RPM as an issue. 

 

I supposed that since areal density is so high on modern drives that even 5900 rpm drives have sequential rates near 150MB/sec.  That said, the Parity drive is probably a very busy drive in this system and at 5900 RPM will be the bottleneck in the system

 

Given I don't want to buy another drive at this time - sounds like i should go with the 3TB for parity for now, loose the 4TB from the system?  Or...just live with a small difference in performance?

 

Thoughts?

 

Thanks in advance...

[garycase]

The key performance difference with your 5900rpm parity drive isn't the sustained data rate -- it's the seek time difference.  I'd just live with the difference, given that it's your only 4TB drive ... no reason to sacrifice the drive.

 

What you may want to do is simply buy a 7200rpm 4TB unit the next time you want more storage -- and make that the parity drive and use your current parity drive as additional array storage.

 

By the way, if all of your drives have 1TB platters (your config doesn't list the make/models so I can't tell) then that 5900rpm unit is also causing your parity checks to be about 20% slower than they could be.    That would still be true if you moved it to an array drive.    The only way to eliminate that bottleneck would be to indeed just not use it and simply go to all 7200rpm drives with 1TB platters.    If your 3TB drives have lower areal density platters, then the 5900 rpm unit isn't a bottleneck at all for parity checks and rebuilds, since a 1TB 5900rpm unit easily matches (actually exceeds)  the sustained data rate of 3TB drives with 750GB platters.

 

 

[jeffreywhunter]

Excellent feedback.  Here's my inventory:

 

http://my.jetscreenshot.com/12412/20150325-92mm-32kb

 

Note the USE column, for which drives I'll be using in the Unraid.  All 1000 GB platters except for the 2TB Hitachi drives which are 667 GB.  Also found an error, the 3TB drives are also coolspin (5700).  So its a mix.

 

Seems like the 4TB as the Parity isn't a huge issue anymore.

 

Know anyone who wants to buy some drives!

 

 

 

 

[garycase]

Given your inventory list, I'd definitely just keep the 5900rpm drive as your parity drive, as it's not going to have any impact on parity check speeds with the other drives in the mix [it's even faster than the 2TB 7200rpm unit].

 

Up to you whether you want to buy 7200rpm units as you expand the array ... but quite frankly I wouldn't bother.  I like the lower power, cooler running drives that run a bit slower => and with 1TB (or larger) platters the sustained data rates are VERY good even at those speeds.

 

 

[jeffreywhunter]

Thanks to all who answered this post.  Very helpful.  This is a good forum and I'm looking forward to launching this server.  I'm moving from 8TB WHS on WIN7 which decided to forget that I had a Raid 5 array.  Thank God for backups!