Hello Guys,

 

I built my system a while ago but was running it without parity drive because all I had in it was replaceable data. But now I have some very important data in unraid shares and crash plan backup and I realise its time to put in a parity drive to protect the data. I have 2x 2 TB WD red NAS drives for the array.

 

Do I need to put in an expensive NAS drive for the parity disk or can I throw in a cheaper 2.5" drive pulled out of a external HD.

Hello Guys,

 

I built my system a while ago but was running it without parity drive because all I had in it was replaceable data. But now I have some very important data in unraid shares and crash plan backup and I realise its time to put in a parity drive to protect the data. I have 2x 2 TB WD red NAS drives for the array.

 

Do I need to put in an expensive NAS drive for the parity disk or can I throw in a cheaper 2.5" drive pulled out of a external HD.

in theory any drive will work (as long as it is at least as large as the largest data drive)..  However since the parity drive is involved in all writes to the system if it is slow it will degrade performance.  It will also be the most stressed drive as it is used the most.

 

On my own system I tend to use NAS quality drives for parity, and am less discerning for data drives.

Do I need to put in an expensive NAS drive for the parity disk or can I throw in a cheaper 2.5" drive pulled out of a external HD.

 

I'd hardly call NAS drives "expensive" at today's prices.  A 2TB WD Red is $79.99 at Amazon 

https://www.amazon.com/Western-Digital-Red-WD20EFRX-SATA-6GB/dp/B01LWYSGV7/ref=sr_1_43?s=pc&ie=UTF8&qid=1486196752&sr=1-43&keywords=WD+Red

 

Nevertheless, any drive that's >= the size of your largest data drive will work as a parity drive.

 

As noted above, if the drive is a slow one (e.g. a notebook drive is typically slower than a 3.5" desktop unit), then it will slow down your writes.  In fact, ANY parity drive will make your writes a good bit slower than they are now, since writes become more complex due to maintaining parity.

 

In most cases, however, I do NOT agree with this comment:

 

... It will also be the most stressed drive as it is used the most.

 

The parity drive is indeed used for every write.  But it is not used at all (or even spun up) for reads.  So the data drives, which are clearly used for both every write to the drive AND for every read operation, are generally used a good bit more than parity.

 

 

 

 

... But now I have some very important data in unraid shares and crash plan backup and I realise its time to put in a parity drive to protect the data.

 

By the way, your comment implies you DO backup your data, but be sure you don't stop doing this just because you add a parity drive.  While it's a good idea to add fault tolerance to your UnRAID server, that is NOT a substitute for maintaining backups of any data you don't want to lose.

 

... But now I have some very important data in unraid shares and crash plan backup and I realise its time to put in a parity drive to protect the data.

 

By the way, your comment implies you DO backup your data, but be sure you don't stop doing this just because you add a parity drive.  While it's a good idea to add fault tolerance to your UnRAID server, that is NOT a substitute for maintaining backups of any data you don't want to lose.

 

 

absolutely.

 

irreplaceable data goes on to a external disk on top of the crashplan backups.

The parity drive is very important for write performance. In my system, it is by far the most written to drive. While a slow data drive will mean shower writes to that drive, a slower parity will mean slower writes to every drive.

 

However, parity contains no data and is only relied upon for data when another disk fails (or appears to fail). You could argue it is the least important drive in the system.

 

I tend to use 7200 RPM on my parity drive. As if I had a drive that was fast but not quite as reliable (Seagate), I'd consider that for parity and use my "best" drives (HGST) for data. (When I say not quite as reliable, I mean based on other drive failures, forum reputation, or BackBlaze reports. I would not use a drive in the array that I personally found to be unreliable or had concerning smart issues).

... In my system, it is by far the most written to drive.

 

    That's clearly true in EVERY UnRAID system, since every write involves the parity drive.

 

... In my system, it is by far the most written to drive.

 

    That's clearly true in EVERY UnRAID system, since every write involves the parity drive.

 

Maybe not. On some arrays the cache drive gets more writes. Since I dnt cache writes, my parity drive gets the most.

The question here was about the parity drive vs. array data drives -- i.e. whether the parity drive should be of the same quality.

 

With regards to data being written to the array, the parity drive absolutely ALWAYS gets the most writes -- even if you have a cache, since any data cached for a protected share will later be written to the array via the Mover.  If EVERY share is cached, then indeed the cache will have the same number of writes as the parity drive (and would, of course, have more if there are unprotected shares on the cache drive -- but this is a bit outside the discussion).

 

So while the cache drive CAN have the most writes, with regards to the protected array, the parity drive ALWAYS has the most writes of any drive.

 

Thanks for the input guys.

 

Do you have recommendations for the Parity drive for me. My data drives are WD red but I don't think they are 7200 rpm.

Thanks

I'd just use another WD Red.  These are excellent drives and work very well with UnRAID.

 

If you want a 7200rpm unit, either use a WD Red Pro, or a HGST NAS drive.

 

You may want to consider buying a larger drive than your current data drives, so you'll be able to use larger drives when you expand your array.  No need to jump all the way to 8TB, but a 3TB or 4TB unit would give you a nice bit of "headroom" for future expansion.

 

 

If all other drives are 5400, 7200 RPM parity would not make a big diff.

 

Gary - 6TB reds didn''t fare so well on Backblaze Report recently. 11% failure rate. 4TB look excellent.

 

LOOK HERE

 

If all other drives are 5400, 7200 RPM parity would not make a big diff.

 

Gary - 6TB reds didn''t barte so well on Backblaze Report recently. 11% failure rate. 4TB look excellent.

 

LOOK HERE

They work well so far for me.  But I prefer the HGST NAS 6TB drives.  I only am using the WD REDs now because I have a server that only had WD REDs in it and I am keeping drives from the same manufacturer in it.  It is mostly 4TB REDs with a few 6TB thrown in currently.  Was going to slowly swap out the 4TBs for 6TBs as I need more space.

If all other drives are 5400, 7200 RPM parity would not make a big diff.

 

That depends on how the system is used.  If there are multiple users and the system is frequently doing multiple simultaneous writes, a 7200rpm parity drive will make an appreciable difference in write speeds, as the better seek speeds of 7200rpm drives will significantly reduce the added delay for the multiple parity accesses during those writes.  It's not the rpm that matters (although that also provides a small benefit in that situation), but the much faster access times as the parity drive goes between the various sectors involved in the different writes.