Linux Storage

Linux Storage Analysis

Specifics - Linux storage analysis

This is Linux storage from the z/VM perspective:

Linux needs to use swapping or all of its initialization pages will remain in memory, which is wasteful.
Swap should be done to virtual disk (not real DASD).
If a Linux server is not swapping, reduce its virtual machine size on z/VM or reduce its storage size on Linux (use CMM - Cooperative Memory Management on Linux).
Reducing the size of the virtual machine on z/VM reduces caching of old data.
Start with 1 small vdisk (100M) and 1 larger vdisk (2G). Set the priority to favor the smaller vdisk. Set an alert if the larger vdisk is used.
Note: In Linux the lower number has the higher prioritization and will be used first.
Use DIAG driver instead of FBA. FBA is 512 bytes. DIAG will group those into 4K pages which reduces I/O by a factor of 8.
Virtual disk can get paged out when not in use (goodness). It has no overhead until 'touched'.
Rule of thumb - if a server is not using swap, it is oversized. If a server is using some swap, it is sized correctly. If a server is using a lot of swap, it is undersized.

If Linux storage is an issue, consider using zVRM

ESAUCD2 - Linux UCD memory analysis. Both screen and report samples:

Real Storage Avail - This shows available RAM not currently in use. If a server shows high availabilty of storage not in use, they may be over allocated (over 5%).

SWAP Storage Used - This shows SWAP space in use. Watch for high real storage availability with no swap.

Storage in Use Buffer - This shows storage in use for data buffers. Watch for greater than 20mb. If this is the case, may need to use CMM (see above) to change storage size on Linux.

Storage in Use Cache - This shows storage in use for page cache.

Error Message - This shows an error message if the threshold has been exceeded or some other error has occurred. (The mail server is a proprietary component and doesn't use swap space.)