How much gain does having a faster parity drive over your regular array drives give you?

 

I have heard mixed responses to this, some say no gain while others say some and I have also heard "only during parity checks."

 

Could anyone clarify? Is there any real gain by having a faster drive like a WD Black as your parity drive if the rest of your array is made up of green/LP drives?

you only gain a benefit when you are writing to more then one data drive at a time. Maybe coping to media drive while a backup to a backup drive or maybe the mover script is running..

 

You could also gain while writing during a parity check or rebuild (although i tend to not do that personally).

 

It is really a personal option based on how you use your server.

 

if you have a server you almost never write to. especially multiple drives at one once, you'll gain almost nothing.

Would a faster parity drive reduce the time it takes for unRAID to perform a parity check? I'm guessing that the bottleneck would likely be the motherboard bus as opposed to the drive/s?

Would a faster parity drive reduce the time it takes for unRAID to perform a parity check? I'm guessing that the bottleneck would likely be the motherboard bus as opposed to the drive/s?

The speed of the parity drive makes very little difference when checking parity.  As already noted, the only time a faster parity drive really helps if if you are regularly writing to more that one array disk at a time.

Would a faster parity drive reduce the time it takes for unRAID to perform a parity check? I'm guessing that the bottleneck would likely be the motherboard bus as opposed to the drive/s?

The bottleneck is probably EITHER the slowest sustained data read speed of the disks involved, or the motherboard bus, or a combination of the two.

 

In my older PCI bus based server, it is definitely the PCI bus, until it gets to the two largest disks.  At that point, they are the only two disks involved. (parity and 1 data drive) It might still be the PCI bus even there... the SATA controller on the MB they use is a first generation one, probably a slow one.

It also helps if you are doing allot of random writes, like a torrent download.

Every little bit helps.  Mostly when you are doing a bunch of tasks on the server simultaneously.

You'll see me mention on the forum that I have a RAID0 parity drive on a caching controller.

 

FWIW with torrents I find it much better (using utorrent on my desktop) to have the client first download to a temp directory on my desktop and THEN move it to unraid when download is complete.  utorrent will do the move automatically so it is fire and forget.  Really helps avoid network contention and thrashing of unRAID.  It also means parity is only spun-up for the move operation and not for the entire download period.  During seed-only activity parity stays spun-down .

FWIW with torrents I find it much better (using utorrent on my desktop) to have the client first download to a temp directory on my desktop and THEN move it to unraid when download is complete.  utorrent will do the move automatically so it is fire and forget.  Really helps avoid network contention and thrashing of unRAID.  It also means parity is only spun-up for the move operation and not for the entire download period.  During seed-only activity parity stays spun-down .

 

That works, or downloading to an unRAID cache drive has the same effect (that's what I do).

FWIW with torrents I find it much better (using utorrent on my desktop) to have the client first download to a temp directory on my desktop and THEN move it to unraid when download is complete.  utorrent will do the move automatically so it is fire and forget.  Really helps avoid network contention and thrashing of unRAID.  It also means parity is only spun-up for the move operation and not for the entire download period.  During seed-only activity parity stays spun-down .

 

Someone just released a utserver plugin for unraid. Why not install that and download the stuff to your cache drive first? This way you get the benefit of still being able to manage your torrents from your desktop PC but once you start your downloads you can put the PC to sleep and the unraid server will handle the rest.