Just wondering, since I already purchased a lot of WD Greens but everybody recommends REDs now for NAS. I'm reluctant to purchase another drive yet. Also I would be able to use a cache drive (still have an old WD 500GB lying around) but I would rather not use a Cache Drive. So does it make a big difference if I use a Green or RED as Parity (for write speed and durability)?

 

All my data drives will be 4TB Greens, already have them here.

I certainly prefer the Reds ... and would buy those in the future.  But I wouldn't bother to buy one just to replace your Green.    I would, however, buy Reds when you need additional drives.

 

I wouldn't bother to buy one just to replace your Green.

 

I agree.

 

 

However, in my particular case/usage pattern, I would certainly purchase a 7200 RPM drive for my parity and the most used drive in the array.

 

In my case I have 7200 RPM parity and DISK 1, which are the most used drives in my array.

Everything else is slower.

 

With my tunings I can burst write to the server at 110MB/s up to 500MB, it slows down bit by bit until I hit around 2GB where it's at 40-50MB/s.

Yeah I was thinking about getting a 4TB 7.2k rpm but that would be a WD Black and those are quite expensive...I wonder if really makes such a huge difference. Your numbers said pretty good. I haven't actually installed my parity drive yet since it will take me at least two more days just to copy the data across. If I knew that write speeds are below 50 MB/s with a Green / Red as Parity I'd definitely would go for a Black, but anything around 50 MB/s would be ok for me.

Write speeds will definitely be below 50MB/s with a green or red as parity -- in fact they'll be below 50MB/s even with a black.    WeeboTech's initial write speeds are due to system tuning that's allowing extensive buffering during the initial writes (up to 500MB) -- note that it then drops to the 40-50MB/s range, and will stay there for the remainder of any large transfers.

 

The benefit of the 7200rpm blacks is the faster access time.  They are not any faster than the Seagate NAS and only marginally faster than the WD Red units in sustained transfer speed.  So just how much benefit you'll see with them depends on the usage pattern of your system.  If you do a lot of small writes, the blacks will help quite a bit;  if your primary use is copying large media files to the server, it's unlikely you'll notice any difference.

 

If you want to significantly improve your parity drive's speed, I'd buy one of these instead of a WD Black:

http://www.newegg.com/Product/Product.aspx?Item=N82E16822178379

With the 8GB integrated SSD cache, this should give you very good write speeds for several GB of data before it would lose the benefits of the cache.   

 

Thanks for the explanation. I will mostly write large files to the array. So as you explained, I wouldn't gain much from the WD Black. I will stay with the Green / Red then. Thanks.

If you want to significantly improve your parity drive's speed, I'd buy one of these instead of a WD Black:

http://www.newegg.com/Product/Product.aspx?Item=N82E16822178379

With the 8GB integrated SSD cache, this should give you very good write speeds for several GB of data before it would lose the benefits of the cache. 

 

The hybrid drives are write thru. The SSD cache is only for reads of the most used LBA's. (Which is a positive aspect).

A drive with a faster spindle speed is better in the parity role. Especially if there are many random writes over multiple drives. i.e. news downloader, bittorrent and any other interactive type of editing.

 

If unraid is just a media storage box, the difference from 5400 to 7200 is negligible.

If you beat the hell out of your server as a main file server like I do, the difference is quite noticeable.

 

What people miss is that basic housekeeping such as updating the superblock also causes the heads to go back and forth updating the journal for writes.  Even if the journal is being updated on disk1, the parity is also being used for reads/xor/writes.

 

As mentioned, you can only write as fast as your slowest drive, but once there are writes with multiple drives that rule is not so cut and dry.

 

In any case, for large continuous writes to a single drive, the parity speed only needs to equal the other drives. A hybrid drive in this role would probably be wasted unless there were allot of reads/writes to a specific set of directories/files over and over.  The benefit would be,  directory LBA's end up being cached. This could have a positive effect, but I'm doubting it would be better then x64 kernel and a large amount of ram caching dentries.

 

In this particular usage pattern, it makes no difference for the expenditure.

 

However the 4TB 7200RPM Hitachi drives do not seem that expensive. I'm planning the upgrade myself.

 

Generally, I get 38-40MB/s as I push more and data to the server. Therefore the average will probably be around 35MB/s for populating the array with parity and 5400RPM drives.

 

You can try to set the md_write_method during the initial population to try and speed it up.

 

Do a search on md_write_method to see various conversations.

http://lime-technology.com/forum/index.php?topic=31472.msg290832#msg290832

 

In this particular usage pattern enabling md_write_method with a faster parity drive will help.

 

It all depends on how the array is used. if it's a copy movie file over the network set and forget, go the most cost effective route.  For me, I use my server for everything. It is the central repository for everything and it's always spinning because of the high usage patterns.