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#26 2018-12-05 21:24:32

seth
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Registered: 2012-09-03
Posts: 8,929

Re: Seperating / and /usr for SSD and HDD system

bind mounts?

Edit: got ninja'd - wasn't meant as an invitation to post "man mount" ;-P

Last edited by seth (2018-12-05 21:25:20)

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#27 2018-12-05 23:58:09

respiranto
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Registered: 2015-05-15
Posts: 390
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Re: Seperating / and /usr for SSD and HDD system

I don't know why, but some time ago, I noticed that is in fact possible to mount a filesystem on two separate locations.  I verified again (ext4, vfat) and it works.  I don't know whether there are any pitfalls, though.

Maybe, behind, a bind mount is done automatically.

However, it is usually a bad idea to mount one partition directly to two directions with different meanings, as the subdirectories may interfere.  And it is likely to lead to confusion, since for each of the mounpoints, half of its subdirectories will not be meant to be accessed through that mountpoint.

Bind mounts are a fine, though, see the reply of progandy.

EDIT: Remove duplicated information.

Last edited by respiranto (2018-12-06 00:00:30)

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#28 2018-12-06 00:08:17

Trilby
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Registered: 2011-11-29
Posts: 20,440
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Re: Seperating / and /usr for SSD and HDD system

respiranto wrote:

I don't know why, but some time ago, I noticed that is in fact possible to mount a filesystem on two separate locations.  I verified again (ext4, vfat) and it works.  I don't know whether there are any pitfalls, though.

Of course it's possible.  But in the situation described in this thread it'd have disasterous results.  As for not knowing the pitfalls ... you go on to elaborate them well.


"UNIX is simple and coherent..." - Dennis Ritchie, "GNU's Not UNIX" -  Richard Stallman

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#29 2018-12-06 17:54:15

drcouzelis
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From: Connecticut, USA
Registered: 2009-11-09
Posts: 4,010
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Re: Seperating / and /usr for SSD and HDD system

Let's be specific. smile

I just built this package: https://aur.archlinux.org/packages/davinci-resolve

It is 1575 MiB (about 1.5 GB).

My root ("/") partition is 30 GB. I install packages liberally, and I usually forget to uninstall what I don't need. tongue Even with DaVinci Resolve and all of those packages installed, my root partition is only 87% full (3.8 GB remaining).

In other words, a 30 GB partition for Arch Linux will be just fine (with the exception of your "/home" directory). And 40 GB will be waaaaaay more than fine. smile

There is no need to separate "/" and "/usr" and "/var" and whatever else. You just need "/" and "/home".

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#30 2018-12-06 21:38:32

/dev/zero
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From: Melbourne, Australia
Registered: 2011-10-20
Posts: 1,202
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Re: Seperating / and /usr for SSD and HDD system

drcouzelis wrote:

Even with DaVinci Resolve and all of those packages installed, my root partition is only 87% full (3.8 GB remaining).

Note that many filesystems (ext4 included) only have good fragmentation resistance when the partition is less than 50% full, roughly.

If you have 26G on the root partition, then I would make sure the root partition can hold at least 50G.

Once any drive reaches 50% full, I think it is time to start shopping around for a bigger drive wink

An 8TB drive with 7.5K RPM is not too expensive these days, no need to be stingy with the size of a root directory, I usually make it ~100G (or that order of magnitude).

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#31 2018-12-07 01:22:34

ngoonee
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From: Between Thailand and Singapore
Registered: 2009-03-17
Posts: 7,190

Re: Seperating / and /usr for SSD and HDD system

drcouzelis wrote:

Let's be specific. smile

I just built this package: https://aur.archlinux.org/packages/davinci-resolve

It is 1575 MiB (about 1.5 GB).

My root ("/") partition is 30 GB. I install packages liberally, and I usually forget to uninstall what I don't need. tongue Even with DaVinci Resolve and all of those packages installed, my root partition is only 87% full (3.8 GB remaining).

In other words, a 30 GB partition for Arch Linux will be just fine (with the exception of your "/home" directory). And 40 GB will be waaaaaay more than fine. smile

There is no need to separate "/" and "/usr" and "/var" and whatever else. You just need "/" and "/home".

You are correct. But there's really no upper limit to what other software can be installed, and proprietary software can be really large. Some of my science/engineering software takes 3-5 GB each.

But yes, a 250GB SSD is more than enough for windows + arch root in general.


Allan-Volunteer on the (topic being discussed) mailn lists. You never get the people who matters attention on the forums.
jasonwryan-Installing Arch is a measure of your literacy. Maintaining Arch is a measure of your diligence. Contributing to Arch is a measure of your competence.
Griemak-Bleeding edge, not bleeding flat. Edge denotes falls will occur from time to time. Bring your own parachute.

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#32 2018-12-07 17:12:12

drcouzelis
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From: Connecticut, USA
Registered: 2009-11-09
Posts: 4,010
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Re: Seperating / and /usr for SSD and HDD system

/dev/zero wrote:

Note that many filesystems (ext4 included) only have good fragmentation resistance when the partition is less than 50% full, roughly.

Once any drive reaches 50% full, I think it is time to start shopping around for a bigger drive

Wait a minute...

WAAAAAIT a minute...

Are you telling me that if I have a 250 GB SSD then I should plan to use only 125 GB? And on my new 4 TB HDD I should plan to use only 2 TB??? That's ludicrous!

...or at least nothing I've ever heard before. Is there a place I can read to learn more about this practice of buying a hard drive and only planning to use half of it?

EDIT: Thank you for the information below! smile

Last edited by drcouzelis (2018-12-07 18:04:01)

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#33 2018-12-07 17:37:02

seth
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Registered: 2012-09-03
Posts: 8,929

Re: Seperating / and /usr for SSD and HDD system

https://opensource.com/article/17/5/int … filesystem
man e4defrag

The 50% figure seems arbitrary (and too low) because it depends a lot on the kinds of files and usages we're talking, but the fuller the disk, the less effective those anti-fragmentation strategies become (and in the extreme case the FS simply *has* to use the last free inodes)

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#34 2018-12-07 23:55:52

ngoonee
Forum Fellow
From: Between Thailand and Singapore
Registered: 2009-03-17
Posts: 7,190

Re: Seperating / and /usr for SSD and HDD system

Is fragmentation even a serious issue with SSDs with their fast access times though?


Allan-Volunteer on the (topic being discussed) mailn lists. You never get the people who matters attention on the forums.
jasonwryan-Installing Arch is a measure of your literacy. Maintaining Arch is a measure of your diligence. Contributing to Arch is a measure of your competence.
Griemak-Bleeding edge, not bleeding flat. Edge denotes falls will occur from time to time. Bring your own parachute.

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#35 2018-12-08 09:13:49

seth
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Registered: 2012-09-03
Posts: 8,929

Re: Seperating / and /usr for SSD and HDD system

"fast RANDOM access times" ;-)
You still have the overhead on the FS (indirections, metadata) but whether fragmentation is a serious issue at all severely depends on which files are fragmented.
Eg. keep in mind that unix systems traditionally rely on a vast amount of small config files in various locations, written at different times (/usr/share/foo/config, /etc/foorc, ~/.foorc) which all need to be read at a process startup and are, as a common data pool, inherently "fragmented" (while each is likely << 4kB) - luckily there's also the file cache smile
On the other hand, if the Megatexture™ files of Super Turbo Turkey Puncher 3™ are heavily fragmented, you'll notice that far more on an HDD than on an SDD.

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