Uneven Read/Write Graphs

[Oubadah]

I've recently purchased a couple of

WD3200BEKT drives, and their read/wite graphs look a little weird to me. I thought this one trough in the first one was strange:



...Until I saw the second one:



I just wanted to check that these uneven graphs don't indicate any problem with the drives. I ask because I'm used to seeing very consistent arcs, and I've never had any looking like this.

[fzabkar]

I don't know about the trough, but the squiggles are a consequence of Variable Bits Per Inch. Each head has different performance characteristics and is individually tuned. This results is slightly different transfer rates for each head.

You can see it more clearly if you repeat the benchmarks, but this time shortstroke the drives to 3GB or 1GB.

See http://malthus.zapto.org/viewtopic.php? ... 1878#p1796

IMHO the more important aspect of your graph is the absence of scatter in the access time data points. This means that there have been no read retries.

BTW, I have often seen results similar to yours in other storage forums.

[Oubadah]

I don't know about the trough, but the squiggles are a consequence of Variable Bits Per Inch. Each head has different performance characteristics and is individually tuned. This results is slightly different transfer rates for each head.

You can see it more clearly if you repeat the benchmarks, but this time shortstroke the drives to 3GB or 1GB.

See http://malthus.zapto.org/viewtopic.php? ... 1878#p1796

IMHO the more important aspect of your graph is the absence of scatter in the access time data points. This means that there have been no read retries.

BTW, I have often seen results similar to yours in other storage forums.

Thanks.

Yeah, I'm used to seeing the squiggles, but normally they'll be pretty much uniform throughout the arc. These are the first drives where I've seen such obvious troughs/straight bits breaking the uniformity.