IOWAIT on Teradata systems

Database
Enthusiast

IOWAIT on Teradata systems

If I query the DBC.ResUsageSpma table (We use Linux based servers)

I find that the IOWAIT can consume up ti 80% of the resource. Now the standard Unix definition for IOWAIT would be that

"Its IDLE time, but at least One process is waiting for IO."

I seem to recall reading on one of the Teradata manuals that anything over 20% IOwait is an issue.

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4 REPLIES
Senior Apprentice

Re: IOWAIT on Teradata systems

Of course a high IOWAIT is bad, but It mainly depends on the duration. Some peaks might be ok, e.g. if you run large loads.
Do you know what kind of work is going on during that time?

Dieter
Enthusiast

Re: IOWAIT on Teradata systems

On our system , today for instance, we average WAITIO of24% with an average BUSY of 44%. At somepoints as overall usage goes up, all the IDLE time is effectively IOWAIT. Does this seem overley high? or would you think it depends on the site, and whats normal for them?
Senior Apprentice

Re: IOWAIT on Teradata systems

I just checked it, according to the recommendations CPUIoWait should be even less than 10% when the system is 100% busy. But this was some years ago before the new Linux system, i don't know if this changed.
Nevertheless you should ask your friendly Teradata support people about that.

Btw, CPUIoWait might be Bynet, too, not only disks.

Dieter

Re: IOWAIT on Teradata systems

Hi, How can I check my system's average I/O wait thru the day. Also, Is there any documentation on what is mean by AMP skew and I/O skew, I see some processes in our system noting 97% as AMP skew.