How bad is it really to install Linux on one big partition?
Solution 1:
The primary (historical) reasons for partitioning are:
to separate the operating system from your user and application data. Until the release of RHEL 7 there was no supported upgrade path and a major version upgrade would require a re-install and then having for instance
/homeand other (application) data on separate partitions (or LVM volumes) allows you to easily preserve the user data and application data and wipe the OS partition(s).Users can't log in properly and your system starts to fail in interesting ways when you completely run out of disk space. Multiple partitions allow you to assign hard reserved disk space for the OS and keep that separate from the area's where users and/or specific applications are allowed to write (eg
/home /tmp/ /var/tmp/ /var/spool/ /oradata/etc.) , mitigating operational risk of badly behaved users and/or applications.Quota. Disk quota allow the administrator to prevent an individual user of using up all available space, disrupting service to all other users of the system. Individual disk quota is assigned per file system, so a single partition and thus a single file-system means only 1 disk quotum. Multiple (LVM) partitions means multiple file-systems allowing for more granular quota management. Depending on you usage scenario you may want for instance allow each user 10 GB in their home directory, 2TB in the /data directory on the external storage array and set up a large shared scratch area where anyone can dump datasets too large for their home directory and where the policy becomes "full is full" but when that happens nothing breaks either.
Providing dedicated IO paths. You may have a combination of SSD's and spinning disks and would do well to address them differently. Not so much an issue in a general purpose server, but quite common in database setups is to also assign certain spindles (disks) to different purposes to prevent IO contention, e.g. seperate disk for the transaction logs, separate disks for actual database data and separate disks for temp space. .
Boot You may have a need for a separate
/bootpartition. Historically to address BIOS problems with booting beyond the 1024 cylinder limit, nowadays more often a requirement to support encrypted volumes, to support certain RAID controllers, HBA's that don't support booting from SAN or file-systems not immediately supported by the installer etc.Tuning You may have a need for different tuning options or even completely different file-systems.
If you use hard partitions you more or less have to get it right at install time and then a single large partition isn't the worst, but it does come with some of the restrictions above.
Typically I recommend to partition your main volume as a single large Linux LVM physical volume and then create logical volumes that fit your current needs and for the remainder of your disk space, leave unassigned until needed.
You can than expand those volumes and their file-systems as needed (which is a trivial operation that can be done on a live system), or create additional ones as well.
Shrinking LVM volumes is trivial but often shrinking the file-systems on them is not supported very well and should probably be avoided.
Solution 2:
The concept of using multiple partitions is that a full one in the the wrong place will not cause the whole system to work unexpected.
Consider a process on the machine filling up a logfile pretty fast up to the point that there is no free space available. On a single-partition machine, this could then, for example, prevent the system to write new data to /tmp. If there is another process that would want to write to /tmp it would probably exit with an error, causing unexpected behaviour.
This can be prevented if you use different partitions for places where users or processes normally write to (/home, /var, /tmp).
I would recommend that you check your old server which folders tend to get big. You can do that on the command line with
du -h -d 1 / 2> /dev/null
You'll see where the most data is accumulated and design your next system appropriately. The "-d 1" limits the output to only one level of folder depth making it more readable.
Solution 3:
The main problem with having a single large partition is that filling the filesystem up it is possible that no login is possible anymore.
The user root has its home folder (/root) outside of /home because of this. If the filesystem is filled up under some circumstances even root cannot log in and cannot repair the system.
This is the reason why you normally create separate mounting points for /var, /tmp and /home to be able to login at least as root to repair the system when one of the other partitions is filled up.
Solution 4:
IMHO, having one partition as / is quite reasonable.
But you can use lvm (logical volume manager). Use all disk as lvm group, but create small logical disks for /,/home,/usr and whatever your sysadmin prefers. Then put some monitoring on, that you know, when your system starts getting full and expand those disks that you need. lvresize and resize2fs is online tools and you can do expansion without restarting server. However you can not reduce disks, so you need to start reasonably small and increase where you see need.
Solution 5:
There are minimal problems around the big-single-partition setup of linux, but it has big rewards.
Changing a partition layout is a little bit hard and risky thing, which you often can't do without long downtimes.
Its only advantage is that you have some protection against disk full problems. But you will find these problems much often. Imagine the situation, if one of your partitions are full, and you can't use the space on the other partitions, even if they are nearly empty!
Some professional system administrators have a total different opinion about this. They are saying, that having multiple partitions can make your system more reliable and you must know before your partitioning, how big your partitions will be. On my opinion, this simply can't be said, it is a terrible drawback on the flexibility on the system, and their real motivation is that they are simply liking to play with the partition maps.
There is a simple system named lvm, which enables the on-the-fly moving/resizing of "partitions" (in its terminology, volumes). But on a single local department server, IMHO it is normally not needed.