# Any reason not to share a read-only \`/nix/store\` mount between servers?
**URL:** https://discourse.nixos.org/t/any-reason-not-to-share-a-read-only-nix-store-mount-between-servers/3657
**Category:** Help
**Created:** [August 8, 2019, 12:50am UTC](https://discourse.nixos.org/t/any-reason-not-to-share-a-read-only-nix-store-mount-between-servers/3657 "2019-08-08T00:50:50Z")
**Posts on this page:** 12
**Page:** 1
### Author:  [@psychic](https://discourse.nixos.org/u/psychic)
#### Post date: [August 8, 2019, 12:50am UTC](https://discourse.nixos.org/t/any-reason-not-to-share-a-read-only-nix-store-mount-between-servers/3657/1 "2019-08-08T00:50:50Z")
Let’s say I have a production system with multiple network application servers for redundancy,
and the application they run is deployed in the `/nix/store`. Is there any reason to duplicate the
store between all the servers?
What would happen if all the application servers had the nix store mounted as read-only, while the rest of /nix was of course, per server i.e. not shared.
Would this be easy to setup? Does it have any potential pitfalls? Theoretically, the nix store paths are read-only, so it seems as if there’s no problem, and yet I haven’t come across a case of such a deployment, and I wonder why is that.
Thanks for the help!
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### Author:  [@alexv](https://discourse.nixos.org/u/alexv)
#### Post date: [August 8, 2019, 1:14am UTC](https://discourse.nixos.org/t/any-reason-not-to-share-a-read-only-nix-store-mount-between-servers/3657/2 "2019-08-08T01:14:56Z")
I am in a similar situation (10+ servers which need identical nix setups) and decided not to put nix store to a shared drive. My reasons are:
1. Speed. Local disks are obviously a lot faster. You WILL notice the difference.
2. Accidents. If something happens to the nix store on a shared drive all the servers are dead.
3. The sqlite database nix uses is notoriously not shared drive (specifically NFS)-friendly. YMMV.
I ended up using one of my servers as master and wrote a simple script that rsync’s /nix (so that the default profile with all the applications is also shared) to the other servers which I run whenever a change to nix setup is made (and I like the result).
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### Author:  [@psychic](https://discourse.nixos.org/u/psychic)
#### Post date: [August 8, 2019, 3:26am UTC](https://discourse.nixos.org/t/any-reason-not-to-share-a-read-only-nix-store-mount-between-servers/3657/3 "2019-08-08T03:26:53Z")
@alexv Thanks for your response!
You raised up valid points.
The idea with rsync is also nice.
Currently I have a script that does a `nix-store --import` on each of the servers.
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### Author:  [@zimbatm](https://discourse.nixos.org/u/zimbatm)
#### Post date: [August 8, 2019, 12:30pm UTC](https://discourse.nixos.org/t/any-reason-not-to-share-a-read-only-nix-store-mount-between-servers/3657/4 "2019-08-08T12:30:36Z")
@psychic are you running a HPC environment? During last NixCon I heard that this was the approach a few of them took. Have a single “master” machine that holds the store and then share `/nix/store` as a read-only NFS volume. I believe the machines would run another distro such as CentOS so the store isn’t needed during boot.
Potentially it should also be possible to mount a secondary store and then use the `--store /mnt/nix` option for the user-land packages.
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### Author:  [@zimbatm](https://discourse.nixos.org/u/zimbatm)
#### Post date: [August 8, 2019, 12:33pm UTC](https://discourse.nixos.org/t/any-reason-not-to-share-a-read-only-nix-store-mount-between-servers/3657/5 "2019-08-08T12:33:33Z")
See also this old thread: [Redirecting to Google Groups](https://groups.google.com/forum/#!searchin/nix-devel/NFS%7Csort:date/nix-devel/GrcHg5C1rk0/foJ03XJdBgAJ)
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### Author:  [@markuskowa](https://discourse.nixos.org/u/markuskowa)
#### Post date: [August 13, 2019, 1:57pm UTC](https://discourse.nixos.org/t/any-reason-not-to-share-a-read-only-nix-store-mount-between-servers/3657/6 "2019-08-13T13:57:27Z")
I am running a small HPC system on NixOS and I was facing a similar question when setting up the system. Despite several reports that exporting the nix-store via NFS can work I could not get comfortable with the idea of tying a central part of the OS to NFS (mainly of all the reasons mentioned by @alexv).
Instead I chose to de-centralize the nix store: My master/login node acts as a cache for the compute nodes (via nix-serve). When I run “nix-build -A” , “nix-shell -p”, or “nix-store --realise” for a specific path or package I get it automatically on the compute node from which I am running the command. In that way there is no need for replicating the whole store for all nodes and I do not need to keep track of a sync status.
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### Author:  [@veprbl](https://discourse.nixos.org/u/veprbl)
#### Post date: [August 13, 2019, 9:49pm UTC](https://discourse.nixos.org/t/any-reason-not-to-share-a-read-only-nix-store-mount-between-servers/3657/7 "2019-08-13T21:49:27Z")
I had run Nix at multiple HPC systems with the store located in my home directory that was mounted either over NFS or over GPFS. I imagine, it should also work fine over AFS. This works well for read only, I’m doing quite a bit of distributed computing with it. Unfortunately it is not possible to write to the nix SQLite database from multiple nodes at the same time – that will quickly result in a corrupt database. Because of that I always do write operations from one specific node.
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### Author:  [@psychic](https://discourse.nixos.org/u/psychic)
#### Post date: [August 15, 2019, 8:03am UTC](https://discourse.nixos.org/t/any-reason-not-to-share-a-read-only-nix-store-mount-between-servers/3657/8 "2019-08-15T08:03:57Z")
I am not running an HPC environment, but it seems like those who do have replied 🙂
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### Author:  [@psychic](https://discourse.nixos.org/u/psychic)
#### Post date: [August 15, 2019, 8:05am UTC](https://discourse.nixos.org/t/any-reason-not-to-share-a-read-only-nix-store-mount-between-servers/3657/9 "2019-08-15T08:05:53Z")
Thanks everyone for your input on this case!
For now I’m going with the no-share internal-cache option, but I will be bookmarking this link for when I need to make the choice again.
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### Author:  [@symphorien](https://discourse.nixos.org/u/symphorien)
#### Post date: [August 15, 2019, 9:34am UTC](https://discourse.nixos.org/t/any-reason-not-to-share-a-read-only-nix-store-mount-between-servers/3657/10 "2019-08-15T09:34:04Z")
About NFS: I have sucessfully run a dozen of remote builders on the same nix store on nfs with the following patch to nix: [Nix Installation Guide - NixOS Wiki](https://nixos.wiki/wiki/Nix_Installation_Guide#NFS)
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### Author:  [@AleXoundOS](https://discourse.nixos.org/u/AleXoundOS)
#### Post date: [June 7, 2020, 7:32pm UTC](https://discourse.nixos.org/t/any-reason-not-to-share-a-read-only-nix-store-mount-between-servers/3657/11 "2020-06-07T19:32:21Z")
Are they running on NixOS?
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### Author:  [@symphorien](https://discourse.nixos.org/u/symphorien)
#### Post date: [June 8, 2020, 8:19pm UTC](https://discourse.nixos.org/t/any-reason-not-to-share-a-read-only-nix-store-mount-between-servers/3657/12 "2020-06-08T20:19:35Z")
No they were on another distro (probably some variant of rhel, but I don’t remember for sure).