Michael Gill

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Oct 15, 2018
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This weekend I ventured into the world of Linux for the first time and am a little confused to say the least. I completed a 13 hours online course and have spent another 10 hours or so reading articles, watching videos and pouring through tutorials. I have have learned a lot in a short time and have a solid understanding of a typical Linux directory and mounted storage. I still don't have a solid understanding of the relationship between directories and partitions, or how to effectively apply Links (Soft or Hard). There are plenty of resources that show how to create directories, how to format and mount a new hard drive (HDD). What I don't find is any information on useful ways to apply that knowledge (or what they are typically used for). I'm a very conceptual person and am hoping someone can help me to understand the fundamentals with file storage on Linux; NOT just the how but the what and the why.

**NOTE: One of my pet-peeves is unclear or vague responses. Please be very clear in your responses to this thread. Please state the question or questions you are addressing and provide references where possible. This is not just for me but in anticipation for future beginners who are having the same issues/questions as me. Please throw caution aside and use as much detail as possible. If there is another thread that explains one aspect of this please post a link to that thread.

My Application/Goal: I had an existing desktop running Windows 10. I wanted to continue to use Windows 10 while simultaneously running a CentOS server (this ruled out a dual boot). To accomplish this I decided to use VirtualBox to start a Virtual machine (VM) running CentOS 7. In my desktop I have a 128GB Solid State Drive (SSD) (that I use as a boot drive for Windows 10), one 750GB Hard Drive (HDD), and three 1TB HDDs. My goal was to install CentOS on the 128GB SSD and then to configure the three 1TB HDDs into a RAID 5 drive.

Now I have a VM running CentOS 7 off of an SSD with three formatted HDDs in a RAID 5 configuration that is mounted. As I started to install software (e.g. Apache, MySQL, PHP, PhpMyAdmin, etc.) I started to realize the files were being saved wherever they wanted to go (I assume this is for optimization purposes). I haven't been able to find any information so far on installing software to a specific directory. I'm also noticing that once software is installed it automatically saves files into that same directory.

Now for my first big question (I know these questions are vague):
  • How do I utilize my RAID 5 drive if everything installs and saves files to default locations?
  • How do I manage where software installs and where software saves files?
Every resource I have watched/read on directories and mounting shows a user how to format a drive and then mount the drive to a directory. In every example only one drive (partition) is ever mounted to one directory. In my configuration I started out with one drive (my SSD) and then added a RAID 5 drive. Before adding the RAID 5 drive everything must have been mounted to the SSD so I assume you can mount several directories to the same partition.
  • How do I mount several directories to my RAID 5 drive? Do I simply copy the files to my RAID 5 partition, umount several directories from their current partition, and then mount them all to my RAID 5 partition? How would I then update fstab (separate lines, each listing the same device/UUID, but with a different mount point/directory listed)?
  • What happens if at a later date one of my directories (for example /var/) becomes full and there is no more room on the current SSD or HDD to extend it, how do I move that directory from the existing partition to a new, larger one?
I learned about soft links and hard links but other than describing them as analogous to shortcuts in a Windows OS, none of the resources I have come across give practical applications for either.
  • What are some common uses for links in Linux?
  • Say I have files in a directory stored on my SSD but I wanted to move those files to my RAID 5 (for security). Can I then somehow use links to link those files back to the original directory? For example, say I wanted to move the entire /var/log/ directory. Can I create a /log/ directory on my RAID 5 Drive (copy all of the files from /var/log/ to /raid5/log/ and delete /var/log/) and then create a hard link in /var/ to /raid5/log/? One big concern with moving or linking files/directories is breaking references to software than need specific files to run.

Hello Michael and welcome to linux.org :)

Questions beyond my paygrade so I won't attempt to help.

We have a few Sysadmins here and some are experienced in CentOS, so I expect one or more will be along soon enough.

Good luck and I will watch this Thread with interest and perhaps learn something.

Chris Turner

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