Quote:
Originally Posted by marius09
hi,
i order to reduce the wa (iowait)there are several thing to be done:
-RAM increase -in order to have mnore buffer
-change the disk with a fater disk.
If i like to backup the file system from this host to elshwere outside this server,adding RAM will reduce the wa?
|
The iowait parameter is the time spent by processes for I/O to complete---waiting for read heads to reach the right spot on a disk for reading or writing or, even worse, waiting for networked storage to respond. When I would see high iowait times on systems, it normally had to do with an application that was doing huge amounts of I/O directed at a single disk. Looking at the I/O queue depth for the disk would show huge numbers. On Linux, you can get comparable information by looking at the transactions/sec obtained by the "iostat" command. Back in the day... a queue depth of 50 was considered maxed out; I'd sometimes see sluggish systems with queue depths in the hundreds. (Time to talk to the developers about re-jiggering the application's file layout.) Finding a way to spread the I/O across multiple disks would, generally, help immensely. Now that we have single disks with capacities that exceed what used to require a 7ft tall 19" data center cabinet full of disks, directing all of an application's I/O at a single disk is now the norm than the exception.
Adding more RAM to allow more caching might help but, if the application(s) are doing random reads, caching may not help much---the cache contents may be useless for the next read.
Moving data to faster disks will help but I haven't seen 10K and 15K RPM disks on the market for years.
IMHO, finding a way to spread the I/O around across many devices is the best bet. I've worked with DBAs to set up databases where the tablespaces for data and the indices for that data were spread across on different disks (tablespace A and indices for A were never on the same disk) on an Oracle database server---it was apparent when a junior DBA broke that rule when setting up a new application's data. Check your applications' configurations and see if there's a means of moving some of the data to other disks.
HTH...
