Yet another win for Systemd.
Target disk mode is fantastic, I'm thrilled to see this coming to Linux
this post was submitted on 31 Oct 2023
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Worked in IT, target disk mode is a life saver when you have to recover data from a laptop with a broken screen/keyboard/bad ribbon cable and don't want to take apart something held together by glue.
It's a nice feature. I used it a few times on old Macs with external FireWire hard drives for booting a different OS or troubleshooting.
Soon we'll be debating whether we call it systemd/linux or gnu/systemd.
Red Hat: "we put the D in your System"
Oh, another arm growing.
This seems like a win for almost all distros
Link to the post (for accessibility and follow-up in the thread): https://mastodon.social/@pid_eins/111324093735348164
Pull request: https://github.com/systemd/systemd/pull/29748
Yay, yet another storage protocol over the network.
Not a storage protocol over the network, but yes :P
“ via NVMe-TCP (in case you wonder what that is: it's the new hot shit for exposing block devices over the network, kinda like iSCSI…”
So….?
The protocol already existed. This made it convenient to boot from it
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Can someone eli5 pls?
"target disk mode", which this claims to be taking a lot of inspiration from, pretty much turns your computer into an external harddrive - so you can connect another machine to it for direct access. This appears to be trying to accomplish the same, but over the network.
If you've ever stuffed up a machine so badly that the best idea you could come up with, was to take the harddrive out and work on it from another machine - this pretty much allows you to do that. But instead of taking the drive out and putting it an external drive enclosure, you just ask the stuffed up machine to act as the external drive enclosure.
Great answer
Oh okay. Thanks for the simple explanation :)
same, i have no idea what any of that means and i use runit
runit gang !
From what I understand it's basically like a "thin client" type of thing where the client loads the Kernel from local storage up to a certain point and then boots into a rootfs that is somewhere else on a remote server.
Kinda like pxe boot?
Similar but in this case the Linux Kernel/Init System act as the PXE firmware so you don't need a TFTP Server to load initramfs and a Kernel image. And you don't need a NFS or Samba server because the Server has the drive with the rootfs already exposed to the network.
Basically, your system, if asked to, will boot into a limited mode where it exposes its drives over NVMe-TCP. It's like taking the hard drive out and putting it into a different PC, but over the network.
You assessment isn't entirely correct as this is indeed related to systemd. Read the PR https://github.com/systemd/systemd/pull/29748
@TCB13 services aren't systemd-related just because they are launched by systemd.
A service by itself shouldn't be systemd, it should be implemented separately and run under systemd. However, this is using the systemd target subsystem which is a little more specific.
Exactly my point. Thanks.
@winterayars systems targets were formerly known as runlevels, and this particular one probably could also work with init= because what else could you possibly run at the same time?
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How do you think file systems would be handled? Apple’s SCSI/FireWire/USB/Thunderbolt Target Disk Mode just made all disks available over the interface in a filesystem-agnostic manner. Would I be able to see my ext4 boot partition, ZFS arrays, and any attached volumes?
As with Apple's implementation, filesystems aren't handled - whatever device you connected with would see block devices, essentially no different from a physical disk in your system.
Is this like booting over pxe? Is nvme tcp widely supported on motherboards?
No, this has nothing to do with your motherboard. Once you reach the boot menu you'll be able to pick your OS and alternatively systemd-storagetm. If you chose the the latter then your disks will be available to other machines over NVME-TCP. Just like Apple.
The problem of keeping comparing and doing analogies with apple shit stuff is that many of us have no idea what tech of magic apple does, so saying things like "just like apple" is a completely useless phrase that gives zero info whatsoever about anything.
So I could mount and chroot over TCP to fix problems? Looks a little more complicated at this point than fstabbing an iscsi target, but I imagine that'll improve. https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/9/html/managing_storage_devices/configuring-nvme-over-fabrics-using-nvme-tcp_managing-storage-devices
Sweet.
The PR aims to make it easy and simple.
So when it's booted it will just advertise the storage to the LAN over nvme-tcp protocol?
Not "booted", you won't be booting your full OS. It's just an option on the boot menu that launches systemd and a small program that does the magic and nothing else.
But is it running at the same time as a an OS or is it just a device without an OS running, sharing storage?
So NAS without any controls. Yay?
trivial to set up NAS with minimal overhead, plus you can boot any pc into this once it's standard, which would be nice for rescuing when you fuck something up: rather than fiddle around with rescue mode or digging out the drives you just boot into this mode and access the drives from your laptop or whatever.
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So share drive / simplified NAS, no?
Kind of... but you're directly accessing the hard drive like iSCSI does. Way less latency, no high (and slow) protocols like SMB are used.
NVMe/TCP is an extension of the NVMe base specification that defines the binding of the NVMe protocol to message-based fabrics using TCP. The rules for mapping NVMe queues, creation of NVMe-oF capsules, and the methods used to deliver the capsules over the TCP fabric are described in the NVMe/TCP Transport Specification. By binding the NVMe protocol to TCP, NVMe/TCP enables the efficient end-to-end transfer of commands and data between NVMe-oF hosts and NVMe-oF controller devices by any standard Ethernet-based TCP/IP networks. Large-scale data centers can use their existing Ethernet-based network infrastructure with multilayered switch topologies and traditional network adapters
- https://infohub.delltechnologies.com/l/nvme-nvme-tcp-and-dell-smartfabric-storage-software-overview-ip-san-solution-primer-1/what-is-nvme-tcp/
- https://nvmexpress.org/wp-content/uploads/March-2019-NVMe-TCP-What-You-Need-to-Know-About-the-Specification.pdf
- https://nvmexpress.org/answering-your-questions-nvme-tcp-what-you-need-to-know-about-the-specification-webcast-qa/
So like, grubd boot menu? And from there I can boot over a location on my nas for example? I set up ipxe a couple weeks ago but it couldn’t load over my thunderbolt to 10g nic. Would this help?
So this is a service aimed at exposing disks as nvme-tcp boot targets on boot of the system? I mean I love it, I wonder if this could be used to help with a chicken and egg problem I've had with building clustered systems easier. So far I either need a running service to host a network file system (like NFS or CEPH), or I need local disks that bootstrap the clustered storage environment.
And why would this need systemd of all things? Should basically be doable over something like SSH / TFTP, right?
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