Author: Dag-Erling Smørgrav

Benchmarking Advanced Format drives

Important: due to a bug in my benchmark program, the tps numbers in this post are incorrect. See here for the correct numbers.

In the previous post, I discussed Western Digital’s “Advanced Format” drives and the problems caused by their misreporting their real, physical sector size.

I wrote a benchmark utility to demonstrate the performance penalty of unaligned accesses and uncover a drive’s physical sector size. What it does is write blocks of zeroes varying size at regular intervals. For each block size, it writes a total of 128 MB at intervals of four times the block size, and at an offset that varies from 512 bytes up to half of the block size. Continue reading “Benchmarking Advanced Format drives”

Exploring WD Advanced Format drives

I’ve been playing with WD Green disks, trying to solve the 4,096-byte sector problem. To summarize, Western Digital have started to move from 512-byte sectors to 4,096-byte sectors in order to reduce overhead and thereby increase the amount of data that can be stored on the same amount of platters with the same density. These disks (specifically, the EARS and AARS series) emulate 512-byte sectors for compatibility with older BIOSes and operating systems, but the problem is that they report 512-byte logical and physical sectors instead of 512/4,096.

If the length of a write operation is not a multiple of 4,096, or it does not begin at an address divisible by 4,096, either the beginning or the end of the operation, or both, will cover only part of a sector. This requires the disk to do a read-modify-write operation, meaning that it has to read a complete 4,096-byte sector, update parts of it, and write it back. This is extremely inefficient, as I will demonstrate later. Continue reading “Exploring WD Advanced Format drives”

Anathem

I just finished Neal Stephenson’s Anathem—highly recommended! Like most of Neal Stephenson’s novels, it is full of little gems. There were none that stood out as much as the passage in The Confusion where Stephenson manages to place his protagonists in a situation where it is completely natural for one of them to say “I certainly did not expect the Spanish Inquisition”, but here are a couple I just had to share.

On why people stopped building particle accelerators:

Erasmas: “I always tend to assume there’s an infinite amount of money out there.”

Arsibalt: “There might as well be, but most of it is spent on pornography, sugar water, and bombs. There is only so much that can be scraped together for particle accelerators.”

On the balance of power between the protagonists’ civilization and their ostensibly extrasolar and probably hostile visitors:

Cord: “Do you need transportation? Tools? Stuff?”

Erasmas: “Our opponent is an alien starship packed with atomic bombs. We have a protractor.”

Cord: “Okay, I’ll go home and see if I can scrounge up a ruler and a piece of string.”