HOWTO: Multi Disk System Tuning

• Index
• Introduction
• Structure
• Drive Technologies
• File System Structure
• File Systems
• Technologies
• Other Operating Systems
• Clusters
• Mount Points
• Considerations and Dimensioning
• Disk Layout
• Implementation
• Maintenance
• Advanced Issues
• Troubleshooting
• Further Information
• Getting Help
• Concluding Remarks
• Questions and Answers
• Bits and Pieces
• Appendix A: Partitioning Layout Table: Mounting and Linking
• Appendix B: Partitioning Layout Table: Numbering and Sizing
• Appendix C: Partitioning Layout Table: Partition Placement
• Appendix D: Example: Multipurpose Server
• Appendix E: Example: Mounting and Linking
• Appendix F: Example: Numbering and Sizing
• Appendix G: Example: Partition Placement
• Appendix H: Example II
• Appendix I: Example III: SPARC Solaris
• Appendix J: Example IV: Server with 4 Drives
• Appendix K: Example V: Dual Drive System
• Appendix L: Example VI: Single Drive System
• Appendix M: Disk System Documenter

19. Questions and Answers

This is just a collection of what I believe are the most common questions people might have. Give me more feedback and I will turn this section into a proper FAQ.

• Q:How many physical disk drives (spindles) does a Linux system need?

  A: Linux can run just fine on one drive (spindle). Having enough RAM (around 32 MB, and up to 64 MB) to support swapping is a better price/performance choice than getting a second disk. (E)IDE disk is usually cheaper (but a little slower) than SCSI.

• Q: I have a single drive, will this HOWTO help me?

  A: Yes, although only to a minor degree. Still, section Physical Track Positioning will offer you some gains.

• Q: Are there any disadvantages in this scheme?

  A: There is only a minor snag: if even a single partition overflows the system might stop working properly. The severity depends of course on what partition is affected. Still this is not hard to monitor, the command df gives you a good overview of the situation. Also check the swap partition(s) using free to make sure you are not about to run out of virtual memory.

• Q: OK, so should I split the system into as many partitions as possible for a single drive?

  A: No, there are several disadvantages to that. First of all maintenance becomes needlessly complex and you gain very little in this. In fact if your partitions are too big you will seek across larger areas than needed. This is a balance and dependent on the number of physical drives you have.

• Q: Does that mean more drives allows more partitions?

  A: To some degree, yes. Still, some directories should not be split off from root, check out the file system standards for more details.

• Q: What if I have many drives I want to use?

  A: If you have more than 3-4 drives you should consider using RAID of some form. Still, it is a good idea to keep your root partition on a simple partition without RAID, see section RAID for more details.

• Q: I have installed the latest Windows95 but cannot access this partition from within the Linux system, what is wrong?

  A: Most likely you are using FAT32 in your windows partition. It seems that Microsoft decided we needed yet another format, and this was introduced in their latest version of Windows95, called OSR2. The advantage is that this format is better suited to large drives.

  You might also be interested to hear that Microsoft NT 4.0 does not support it yet either.

• Q: I cannot get the disk size and partition sizes to match, something is missing. What has happened?

  A:It is possible you have mounted a partition onto a mount point that was not an empty directory. Mount points are directories and if it is not empty the mounting will mask the contents. If you do the sums you will see the amount of disk space used in this directory is missing from the observed total.

  To solve this you can boot from a rescue disk and see what is hiding behind your mount points and remove or transfer the contents by mounting the offending partition on a temporary mounting point. You might find it useful to have "spare" emergency mounting points ready made.

• Q: It doesn't look like my swap partition is in use, how come?

  A: It is possible that it has not been necessary to swap out, especially if you have plenty of RAM. Check your log files to see if you ran out of memory at one point or another, in that case your swap space should have been put to use. If not it is possible that either the swap partition was not assigned the right number, that you did not prepare it with mkswap or that you have not done swapon or added it to your /etc/fstab file.

• Q: What is this Nyx that is mentioned several times here?

  A: It is a large free Unix system with currently about 10000 users. I use it for my web pages for this HOWTO as well as a source of ideas for a setup of large Unix systems. It has been running for many years and has a quite stable setup. For more information you can view the Nyx homepage which also gives you information on how to get your own free account.