Suggestions and ideas about filesystem sizing on Solaris

Remark
This article have mainly historical value as it is created at 2008. Now the situation is quite different, diskspace is much cheaper and you don't need to be precise and careful about sizes. Also RAM is cheaper and in most of the cases you can create swap as 1GB or less.

Preambul

This document is intended to give some ideas and suggestions how to size the filesystems (and slices) in Solaris OS. Use it with cautious and do not forget to consult with official SUN documentation and your company documents, related to the subject.

Sugestions

    For / (root) filesystem normally you do not need so much disk space. Most of the time you can allocate 256 MB or ever less, but 512 MB is one very good value. Do not attempt to allocate big amount of space and put all directories as /, usr, var, opt, export/home in one filesystem. This may look very sample, but can put you in trouble after some time.
    For /usr filesystem you need average 2048 MB. On time of installation, installer will show you how much you need. Don't put much more space ever if you think to install big amount of software in /usr/local. If this happen, just create separate filesystem.
    For virtual memory i suggest to use this schema:
        < 1 GB – RAMx2.5
        <2 GB – RAMx2
        <4 GB – RAMx1,5
        >4 GB – RAMx1
        Here you should get above just as starting point, because many applications have own requirements. For example Oracle+SAP need swap to be four times RAM, almost independently of size of real memory, but Oracle itself (if it's alone) “prefer to live” in RAM.
    For /var filesystem you can allocate as minimum 512 MB, but if you expect big log files – from system, applications, etc, you should allocate more. The same is true if you expect long life and many updates on your system. Do not forget log rotate utilities, they can help you save some disk space. If your server will be used for jobs, generating big amount of data in /var as mail server or print server you can allocate more disk space, but because most of the print and mail software use /var/spool you can create dedicated filesystem for this purpose.
    Normaly /tmp filesystem is “part” of swap, but for some products as Oracle you can set dedicated filesystem. Normally 512 megabytes are enough.
    For /opt filesystem you should decide the size by self, because in this filesystem normally in Solaris are located installations of external software. 256 MB should be enough for many purposes, but some software (Oracle by example) can fill up to 1.5 GB (or more) only for executable files.
    And last but not least /export/home. Do not set this filesystem very big. Later if it's need you can move home directories and files to new filesystem or create new one like /export/home2 for new users


Ideas

•     Do not allocated entire disk even if you use some volume manager because later when you need diskspace for new filesystem or extend existing one can be hard to get new harddisk
•     Get indeep knowledge about the applications will run on this machine for better filesystems sizing
•     Do not oversize your filesystems and do not set them as little as possible. 20-30% over from the requirements is OK as general rule