Ramroot – Run Arch Linux Entirely from RAM (2017) • Hacker News Board

Re: Ramroot – Run Arch Linux Entirely from RAM (2017)

#31

Post by jandrewrogers » Thu, Jun 20, 2019, 4:50 PM UTC

cjbprime wrote: post #19

I wonder whether this achieves anything performance-wise that just cat'ing every file to /dev/null to warm up the buffer cache wouldn't achieve. In theory, the kernel uses a buffer cache that will hold on to disk pages until they're invalidated by writes. It'll evict the cache if there's memory pressure. But this setup will presumably just crash if there's memory pressure, so that doesn't seem like a win for the RAM…

One of the big advantages is that you do not need to install file systems on your storage for single purpose servers, which allows your application to run on top of the raw block devices. Databases and similar run much better in this configuration (assuming they support raw block devices), especially if you are running on top of a hypervisor.

Re: Ramroot – Run Arch Linux Entirely from RAM (2017)

#32

Post by jabl » Thu, Jun 20, 2019, 4:53 PM UTC

LinuxBender wrote: post #7

I would love to see this feature added to CentOS/RHEL. In the past, we used NFS Diskless which is anything but diskless. Hacking together an initrd that loads everything into ram is, well, hacky. To have a dracut function or a toggle to enable this would be great for lightweight deployments, testing, labs, vagrant, etc... I'm sure that RHEL must have been contemplating it because there is /etc/sysconfig/readonly-root…

We use warewulf (via openhpc) for diskless centos 7 compute nodes at work. Basically initramfs creates a tmpfs, downloads the OS image to it, switches root to it.

Re: Ramroot – Run Arch Linux Entirely from RAM (2017)

#33

Post by jerf » Thu, Jun 20, 2019, 4:53 PM UTC

cjbprime wrote: post #19

I wonder whether this achieves anything performance-wise that just cat'ing every file to /dev/null to warm up the buffer cache wouldn't achieve. In theory, the kernel uses a buffer cache that will hold on to disk pages until they're invalidated by writes. It'll evict the cache if there's memory pressure. But this setup will presumably just crash if there's memory pressure, so that doesn't seem like a win for the RAM…

I can't hard-core prove anything, but I've read the theory on how if I'm accessing warm disk cache, putting things into a RAM disk shouldn't speed them up, and every time I've done it and tested it, putting things in a RAM disk is faster than having it on disk, even when the very act of copying the stuff into RAM should definitely have just warmed everything up just before the test. I've not done it very often, but every time I've tried it in the last ~15 years it's been the case. I don't know exactly why. I don't think I've done this test with my NVMe disk, though. Nominally, since the entire point of this exercise is that we never physically touch the drive it shouldn't matter what sort of drive it is we aren't touching, but reality and theory can differ.

Re: Ramroot – Run Arch Linux Entirely from RAM (2017)

#34

Post by igou » Thu, Jun 20, 2019, 4:56 PM UTC

I remember this feature on Xubuntu circa 2009. Not sure why this is noteworthy.

Re: Ramroot – Run Arch Linux Entirely from RAM (2017)

#35

Post by benj111 » Thu, Jun 20, 2019, 4:58 PM UTC

"Please note that this prompt (y/N) defaults to yes with a 15 second timeout if 4G or more of RAM is detected"

I understood the capitalisation to indicate the default. Or does the default change? That seems bad if you're intending to wrap this in a script.

Re: Ramroot – Run Arch Linux Entirely from RAM (2017)

#36

Post by puppetmaster » Thu, Jun 20, 2019, 4:59 PM UTC

agumonkey wrote: post #26

puppetmaster wrote: post #17

Many OS out there take advantage of RAM Disks. Alpine Linux for instance allows you to boot your root device on ram as a default. SmartOS runs a boot image completely on RAM, and keeps your storage free for a few configs and VMS. Virtually all network booted computers run their OSs from RAM. If you have never pxe booted a machine, it is a beautiful experience once you overcome a few challenges: easy upgrades and roll…

Never having finished Home pxe setup is a great sadness of mine.

Turn that sadness into joy! Even an RPI can host your TFTP and your boot files... Today!

http://ipxe.org/start has all the info you'll need.

Re: Ramroot – Run Arch Linux Entirely from RAM (2017)

#37

Post by wayoutthere » Thu, Jun 20, 2019, 5:08 PM UTC

puppetmaster wrote: post #17

Many OS out there take advantage of RAM Disks. Alpine Linux for instance allows you to boot your root device on ram as a default. SmartOS runs a boot image completely on RAM, and keeps your storage free for a few configs and VMS. Virtually all network booted computers run their OSs from RAM. If you have never pxe booted a machine, it is a beautiful experience once you overcome a few challenges: easy upgrades and roll…

Ditto the love for PXE — booting from a SAN appliance stocked with a few dozen fast SSDs is amazing. When I was doing big VMWare deployments, I had a PXE bootstrap setup that helped me build an entire 40-node cluster from bare metal in an hour.

Even in the event you have to use some secure zone crap, it’s pretty trivial to build since all PXE requires are dhcpd and tfptd — which are often available by default on nearly any *nix variant.

Re: Ramroot – Run Arch Linux Entirely from RAM (2017)

#38

Post by wayoutthere » Thu, Jun 20, 2019, 5:19 PM UTC

imtringued wrote: post #21

wil421 wrote: post #18

I believe FreeNAS does something like this during startup. You can “install” it on mirrored USB drives in case you run out of power. The redundant USBs are used to install the OS back into RAM. An extra USB in case of corruption and they’re way cheaper than SSDs. I’m assuming you still need to write config files back to the USB. FreeNAS prefers ZFS so it’s RAM hungry anyway. The article recommend 500mb more than you…

SSDs cost 26€ for 128GB and offer significantly more performance and reliability. USB drives are not significantly cheaper.

USB thumbdrives are far more portable than NVMe or PCIe SSDs though. Performance doesn’t matter too much in this type of setup; once the OS is loaded into RAM it shouldn’t hit the thumb drive again.

Re: Ramroot – Run Arch Linux Entirely from RAM (2017)

#39

Post by v8engine » Thu, Jun 20, 2019, 5:24 PM UTC

https://en.wikipedia.org/wiki/List_of_Linux_distributions_th...

I came to know about this from Puppy Linux.

Re: Ramroot – Run Arch Linux Entirely from RAM (2017)

#40

Post by cjbprime » Thu, Jun 20, 2019, 5:42 PM UTC

jerf wrote: post #33

cjbprime wrote: post #19

I wonder whether this achieves anything performance-wise that just cat'ing every file to /dev/null to warm up the buffer cache wouldn't achieve. In theory, the kernel uses a buffer cache that will hold on to disk pages until they're invalidated by writes. It'll evict the cache if there's memory pressure. But this setup will presumably just crash if there's memory pressure, so that doesn't seem like a win for the RAM…

I can't hard-core prove anything, but I've read the theory on how if I'm accessing warm disk cache, putting things into a RAM disk shouldn't speed them up, and every time I've done it and tested it, putting things in a RAM disk is faster than having it on disk, even when the very act of copying the stuff into RAM should definitely have just warmed everything up just before the test. I've not done it very often, but e…

Interesting! Did you make sure there aren't any writes happening in the warm disk cache case, even for things like atime?