Comments on: Analyzing I/O performance in Linux

By: Nick Anderson

Nick Anderson — Tue, 27 Apr 2010 17:21:34 +0000

@Roger Themocap – Ah your right. I screwed up when putting my equations into http://www.codecogs.com/components/equationeditor/equationeditor.php to generate the images. Ill get that fixed. FYI its the one for %w thats wrong, should be .503 = 1166.53/(1150.08+1166.53). Thanks for the correction

By: Nick Anderson

Nick Anderson — Tue, 27 Apr 2010 17:17:58 +0000

@phil – Yeah, your write it can be misleading i suppose. In my head I was just thinking Input Output OPeration Kind of like saying your ATM PIN Number (Personal Identification Number Number). I should probably change it up in the post. Thanks for the input.

By: Roger Themocap

Roger Themocap — Tue, 27 Apr 2010 16:48:14 +0000

The numbers in the equations for %r and %w are the same. The results are different.

By: phil

phil — Tue, 27 Apr 2010 13:33:37 +0000

Nice write up. One point to make though, there really is no such thing as an IOP singular. IOPS means IO Operations Per Second. The “OP” part is not short for OPeration. Leaving off the “S” is nonsensical. It’s like PPS in the network space (or hopefully, KPPS). Singular is just IO (for either “I/O Operation” or just I/O sans “/” for the lazy).

By: Nick Anderson

Nick Anderson — Sun, 25 Apr 2010 15:34:20 +0000

@Baylink, hey no problem everyone has cranky days. Thanks for the correction. As for the captcha, I agree. It was the least obnoxious one I could find. Props to http://clickcha.com/ the author.

By: Baylink

Baylink — Sun, 25 Apr 2010 15:16:05 +0000

My apologies for the tone; yesterday was kindof a cranky day.

Nice bits in the rest of the piece.

And I like your captcha.

By: Nick Anderson

Nick Anderson — Sun, 25 Apr 2010 14:29:35 +0000

@Tormak – Thanks for the comments! You are right about noting sata is only 1/2 duplex. I thought about mentioning it but didn’t want to get deep into that discussion. Since you bring it up, Ill toss it in.
As for tuning file systems, that does seem like it would be a good read. In fact I noticed my example file system could use some tuning. If I can get some good data from doing that I may write a file-system tuning follow-up.

By: Nick Anderson

Nick Anderson — Sun, 25 Apr 2010 14:12:43 +0000

@Vonskippy – Thanks I’ll fix it.

@Baylink – Yes, I meant to say Transfers per second. I’ll correct it. From man sar – A transfer is an I/O request to a physical device. Multiple logical requests can be combined into a single IO request to the device. A transfer is of indeterminate size.

By: Baylink

Baylink — Sun, 25 Apr 2010 03:17:41 +0000

“It would be good to note” that IOPS are also known as TPS, if it were anywhere close to *true*.

Alas, it’s not. “Transactions per second”, as it’s generally used, refers to a very specific DBMS benchmark, promulgated by the Transaction Processing Performance Council; the TPS-C rating. (They have two others, but the -C is the one most commonly quoted)

Whether you’re that specfic or not, you’re almost certainly still talking about SQL transactions, and each one of those is going to take a *lot* more than 1 IOP. Generally by 2 to 3 orders of magnitude, but 4 isn’t uncommon, and 5 or 6 isn’t unreasonable.

And if your IOPs are taking seconds, my condolences.

By: Vonskippy

Vonskippy — Sat, 24 Apr 2010 18:41:52 +0000

In your first table, you have 5200 rpm drives – it should be 5400 rpm.