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Ramroot – Run Arch Linux Entirely from RAM (2017)

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

#61

Post by ryanmjacobs »

jandrese wrote: post #43
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…

Sadly PXE boot of a modern Linux OS is easier said than done. Gone are the days of just handing out the kernel over tftp and providing a NFS root. SystemD gets super cranky and you can't even boot the thing without setting some undocumented flags.

I highly recommend using pixiecore as an iPXE server -- your remote machines only need to have PXE enabled. Previously, it was a pain in the ass to install the TFTP server and get a DHCP server capable of not binding to every request (and only PXE requests like the standard allows). pixiecore does everything for you in like 10 seconds: https://github.com/danderson/netboot/tree/master/pixiecore. We're using it on-premise to spin up a server rack into stateless Kubernetes nodes. None of the blades have a hard-drive/ssd :)

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

#65

Post by inetknght »

jandrewrogers wrote: post #59
inetknght wrote: post #48

Earlier quoted context omitted.

Do you know of or could list which databases support raw block devices?

Most of your classic closed source RDBMS (e.g. Oracle) had this as an option, no idea if they still do. Some purpose-built cloud databases operate this way because it makes perfect sense in that environment. Many domain specialized databases kernels (e.g. for real-time sensor data models) support or require this. It isn't something I recall seeing in open source but that is probably because it only works if you are d…

I saw and replied to a question on StackOverflow [1] recently which discussed it. That was the first time I've tried using a block device. It was kinda fun.

1: https://stackoverflow.com/a/55737206/1111557

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

#66

Post by gerdesj »

WC3w6pXxgGd wrote: post #11

Why would this be useful?

Many, many years ago (~1995ish) I was tasked with putting in a small network for a factory. I settled on the newly released NetWare 4.0 for the server and ran Cat4 around the place and coax to link the hubs (yes hubs). PCs ran Win 3.11.

One of them had such a shit slow (RLL I think) hard disc, I decided to network boot it instead and saved quite a lot of money.

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

#67

Post by hazeii »

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…

Couldn't agree more, I've got at least a couple of dozen computers (from workstations and thin clients through 486s and Pi's) at home and only the main server and its backup have persistent storage.

Especially useful for Windows; it is rather slower diskless (compared to BSD/linux) but it makes Windows instances disposable.

Takes a bit of effort (more these days, FUVM systemd) but having a RAMdisk + diskless RO /usr is a great way of having computers everywhere all singing the same song.

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

#68

Post by effie »

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…

That is interesting. Could you please describe in short your methodology? Did you try to read/write many small files, or one big file?

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

#69

Post by effie »

bjackman wrote: post #56
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…

Warming up the page cache is in fact already done on modern systems: http://manpages.ubuntu.com/manpages/xenial/man8/ureadahead.8... I'd agree that making ureadahead more aggressive would indeed make more sense than just sticking your roots in RAM. It shouldn't impact your boot time very much and is much more flexible! But maybe there's some special perf benefit to the ramroot approach..

One theoretical benefit is that linux won't evict file data from a ramdisk, but it will evict it from cache and buffers if it thinks they are not needed that much. The kernel algorithms for memory management are very opaque and linux may do some suboptimal decisions, especially when applications are starving for memory.

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

#70

Post by hpcjoe »

jandrese wrote: post #43
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…

Sadly PXE boot of a modern Linux OS is easier said than done. Gone are the days of just handing out the kernel over tftp and providing a NFS root. SystemD gets super cranky and you can't even boot the thing without setting some undocumented flags.

A little tooting of my own horn here, but nyble[1] allows you to build a ramdisk bootable image and kernel, that you can serve trivially with any http server and iPXE. A related project, tiburon[2] allows you to make this JSON db controlled. Still working on documenting them in greater depth, but you can see an example of what nyble can do[3].

[1] https://github.com/joelandman/nyble

[2] https://github.com/joelandman/tiburon

[3] https://scalability.org/2019/05/nyble-ftw-installing-my-ramb...

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