iostat - transactions per second

[Yrrk]

when doing an iostat 5 or similar command, what exactly constitutes a transaction in the tps field?

1. Is writing a file a single transaction or multiple? I am guessing multiple but how many transactions is it or how do you calculate this?

2. What other types of operations are considered a transaction? Renaming a file? Deleting a file (would this be multiple again?)?

3. Is a transaction per second equiv to an io per second? e.g. many drives/raid cards list performance in terms of io's/sec

Thanks!

 

[MikeLacey]

Hi Yrrk,

This might not be of any use to you as the information refers to HP-UX iostat rather than Linux iostat. And it's not an official answer either - just my understanding which may well get shot down by someone more knowledgable.

A transaction is a "disk-transfer" - which is reading or writing a block from a disk.

When a programmer writes to a file that may well translate into many disk-transfers.

Renaming a file will only update the directory entry - one or two disk-transfers at most.

Deleting a file - same as renaming.

And yes TPS is directly equivalent to I/Os per second.

Mike

To err is human,
but to really foul things up -
you require a man Mike.

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