Speed when mixing different drive models/sizes

[BeaverTerror]

I'm buying drives for a new build and have some questions. The current plan is to have three 3TB Western Digital Red drives (5400rpm) to start with, and to expand as necessary in the future.

 

1. I have on hand a couple of 7 year old 500GB 2.5" hard drives ripped out of old broken laptops. Am I correct in assuming that if I add these two old drives into my array, their much slower speed would massively reduce the overall performance of the entire build? If so, is there anything I could use them for in my unRAID build, or am I better off just forgetting about them?

 

2. Compared to using three WD Red drives, would I see any performance gains if I replaced the parity drive with a faster 7200rpm WD Black drive?

 

Thanks for the help.

[trurl]

1) If used in the parity array, they won't affect the normal read/write performance of the other drives. Unlike traditional RAID, each disk is an independent filesystem, so when reading a file, only the single disk that contains the file is accessed, and when writing a file, only parity and the single disk written is accessed. The drives would have some affect on parity checks and rebuilds, but after the check/rebuild had gotten past their size they wouldn't be involved anymore.And you could use them as cache disks. But, I probably wouldn't bother with them myself since they are too old, small, and slow to waste a port on.

 

2) Parity operations will only proceed at the speed of the slowest disk involved. As mentioned in 1), for normal reading, parity isn't involved, and for normal writing, parity and a single data disk is involved.

[BeaverTerror]

28 minutes ago, trurl said:

1) If used in the parity array, they won't affect the normal read/write performance of the other drives. Unlike traditional RAID, each disk is an independent filesystem, so when reading a file, only the single disk that contains the file is accessed, and when writing a file, only parity and the single disk written is accessed. The drives would have some affect on parity checks and rebuilds, but after the check/rebuild had gotten past their size they wouldn't be involved anymore.And you could use them as cache disks. But, I probably wouldn't bother with them myself since they are too old, small, and slow to waste a port on.

 

2) Parity operations will only proceed at the speed of the slowest disk involved. As mentioned in 1), for normal reading, parity isn't involved, and for normal writing, parity and a single data disk is involved.

 

As I understand, all the disks are used when turbo write is enabled. Do these answers still apply with turbo write?

[JorgeB]

With turbo write enable write speed is limited by the slowest disk, reads will still use a single disk.