hibernation on diskless machine - possible?

Paczesiowa

hi,

is it possible to have diskless (nfs root) machine that can hibernate? I think it would work, but I don't want to try and find out later that first couple times I got lucky and then, I'm out of luck and whole fs gets corrupted. I heard that hibernating with mounted readonly media can work (even if files change during sleep) if you sync and drop caches before suspending, would it work for things mounted rw (and being written all the time)?

thanks in advance.

Hu · Administrator Joined: 06 Mar 2007 Posts: 23066

It is acceptable to hibernate while a filesystem is mounted read-write if the hibernating machine is the only thing that writes to that filesystem, and thus the filesystem does not change between hibernation and resume. Since this restriction is imposed primarily by the fact that the hibernated image retains details about the filesystem, and does not discard them on resume, it might not apply for NFS mounted systems. The client can probably cope with the NFS server changing files while the client sleeps, since such changes can happen without notification while the client is awake, too. However, I have not tested this. What type of diskless system do you have that hibernation is worth the effort over a simple halt? Most diskless devices have such a simple purpose that rebooting them is an acceptable alternative.

Paczesiowa · Posted: Sun Feb 01, 2009 12:10 pm Post subject:

I put hdd from my desktop machine to my server (in another room) because it was too noisy. hibernation is nice for not losing all terminals with running things inside. so if I export on server my whole disk as a single mountpoint it should work? how would I secure it from other things on server? file permissions have to be not so secure, so that non-root users on client can work with them. how about other alternatives than nfs?

Hu · Administrator Joined: 06 Mar 2007 Posts: 23066

jordanwb · Posted: Mon Feb 02, 2009 11:12 pm Post subject:

How about using a flash drive for hibernation?

Paczesiowa · Posted: Tue Feb 03, 2009 2:01 pm Post subject:

you mean one of those ssds? can't afford one now unfortunately.

I'll try tonight with ata over ethernet - if I can get it to work there shouldn't be any corruption problems possible.

szczerb · Posted: Tue Feb 03, 2009 2:26 pm Post subject:

I think he meant a normal pendrive or a CF card.

Paczesiowa · Posted: Tue Feb 03, 2009 3:20 pm Post subject:

but how would I "use" it for hibernation? I'd have to put / and /home/ there, which would kill it pretty quickly.

szczerb · Posted: Tue Feb 03, 2009 3:23 pm Post subject:

You just make a swap partition and hibernate to it. (at least that's the basic idea...)

Paczesiowa · Posted: Tue Feb 03, 2009 4:35 pm Post subject:

it it not a technical problem with swap partition. the real problem is that my hibernated system has opened handles to files that can disappear after resume (that's why they tell you not to hibernate with mounted windows partition, if you are going to use windows. but it's much worse when you leave / mounted rw) or change location on disk layout and when I resume my new kernel will probably corrupt something.

szczerb · Posted: Tue Feb 03, 2009 4:42 pm Post subject:

How can an nfs share change the disk layout? Does it have a disk layout at all?

Paczesiowa · Posted: Tue Feb 03, 2009 4:54 pm Post subject:

I don't know and that's the problem:)

szczerb · Posted: Tue Feb 03, 2009 5:13 pm Post subject:

What would happen if you just unmounted the share on hibernation and mounted on resume?

Paczesiowa · Posted: Tue Feb 03, 2009 5:29 pm Post subject:

try it:>
umount /

szczerb · Posted: Tue Feb 03, 2009 6:33 pm Post subject:

Yeah...basicaly that's why I used the "What would happen if ... ?" syntax :mrgreen:

But isn't it a bit different during hibernation?

x22 · Apprentice Joined: 24 Apr 2006 Posts: 208

Disk layout is controlled exclusively by NFS server so no FS corruption can happen this way.

What can happen is client seeing stale data or getting "ESTALE" errors. This risk can be eliminated if you make sure that the files which are mounted through NFS are not modified by the server or another NFS client.

szczerb · Posted: Wed Feb 04, 2009 12:37 pm Post subject:

So basicaly he needs to unmount all shares other than / /home etc. and keep the server on a UPS, right?