Slow post-read speeds when preclearing drives

[Medwynd]

Been preclearing a few 3TB WD Red drives with 3 cycles per drive.  On every cycle on every drive so far I get about half speed post read speeds.

 

Pre-read average: 110-120 MB/s

Zeroing disk average: 120-140 MB/s

Post-read average: 55-65 MB/s

 

Is this normal?  Why would the post read take longer and run so much slower?

[JonathanM]

It's designed that way with random seeks and stuff to really work the drive, in an attempt to weed out defects.

 

There has been a modified script released that speeds it up somewhat, search for faster preclear.

[Medwynd]

That it was doing random vs sequential access for the post read portion was my guess but I wasn't sure.  I'm not really concerned about the duration, I still have a bit before the rest of my servers hardware shows up on my doorstep.  Thanks for the clarification.

[BRiT]

Are you using the unofficial faster preclear or the original preclear?

 

The faster preclear does all the same work but improves the post read speeds.

[Medwynd]

I'm using the original preclear.

[garycase]

What you're seeing is normal => the post-read tends to take about as long as the pre-read plus the clearing cycle put together.

 

Brian's (bjp999) "unofficial faster pre-clear" script modifies the post-read, so it takes about the same time as the other phases.

 

 

[garycase]

... Brian's script is here:  http://lime-technology.com/forum/index.php?topic=32564.0

 

[Medwynd]

Another odd thing I noticed was that I have 2 new 4TB HGST Drives with what seem to be very slow read speeds on the initial pre-reads as reported by my update emails.

 

http://www.newegg.com/Product/Product.aspx?Item=N82E16822145912

HGST Deskstar NAS H3IKNAS40003272SN (0S03664) 4TB 7200 RPM

 

Both drives report calculated read speeds between 88 and 95 MB/s.  Think this is any cause for concern?