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Holysword
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PostPosted: Thu Jan 14, 2016 11:35 am    Post subject: First time SSD - Also, LUKS Reply with quote

Hello there,

So, for the first time in my life I got a machine with SSD and I want to make sure I won't screw up. I am trying to come up with the proper partition scheme:
sda1 - 128MiB - UEFI boot partition
sda2 - rest of the 128GB SSD - rootfs
sdb1 - encrypted (LUKS) for home directory - this is a SATA HDD

My question is, what needs to be in sda2? I am planning to have /tmp in tmpfs, can I have the whole /var in tmpfs too? Will I see a huge performance drop for having /home in an HDD? What else could I move to the (encrypted) HDD safely?

Thanks in advance!
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szatox
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PostPosted: Thu Jan 14, 2016 5:01 pm    Post subject: Reply with quote

Quote:
what needs to be in sda2
Stuff you want top performance for. Hint: media files do not belong in here. What is your goal?
Quote:
can I have the whole /var in tmpfs too
It's supposed to survive rebooting. Nothing is impossible though. Some things are just not worth the effort.
Linux is doing pretty good job caching hard drive in RAM. I doubt you'd actually see significant performance boost replacing HDD with SSD, unless you're doing something that really requires a lot of IO (mangling data sets too big to fit in RAM, like big and loaded databases).

Why won't you just put everything on your SSD and just mount that HDD somewhere under /mnt and optionally link it to $HOME/Downloads or $HOME/Pictures?
Or.... you could install your system on top of LVM. AFAIR it allows you using a fast device for cache backed with a big device. I never used it, but if it's implemented well, it will keep often used stuff on SSD without bothering you with questions ever again.
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Holysword
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Joined: 19 Nov 2006
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PostPosted: Thu Jan 14, 2016 9:37 pm    Post subject: Reply with quote

szatox wrote:
Quote:
what needs to be in sda2
Stuff you want top performance for. Hint: media files do not belong in here. What is your goal?
Quote:
can I have the whole /var in tmpfs too
It's supposed to survive rebooting. Nothing is impossible though. Some things are just not worth the effort.
Linux is doing pretty good job caching hard drive in RAM. I doubt you'd actually see significant performance boost replacing HDD with SSD, unless you're doing something that really requires a lot of IO (mangling data sets too big to fit in RAM, like big and loaded databases).

Why won't you just put everything on your SSD and just mount that HDD somewhere under /mnt and optionally link it to $HOME/Downloads or $HOME/Pictures?
Or.... you could install your system on top of LVM. AFAIR it allows you using a fast device for cache backed with a big device. I never used it, but if it's implemented well, it will keep often used stuff on SSD without bothering you with questions ever again.

I mostly browse the internet, game, and compile things (well, besides portage, but also including portage).

I have never checked out LVM. To be honest, I`m not sure what it is about. Is there any quick introduction to its capabilities I could take a look at?
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szatox
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PostPosted: Sat Jan 16, 2016 9:47 pm    Post subject: Reply with quote

Long story short, LVM is a very high level interface to device mapper. Like in you demand something and LVM figures out how device mapper could do that.
E.g. you tag some device(s) as physical volume(s), add it/them to an LVM pool, and then you can demand a slice of some size from that pool and LVM will check for not-currently-mapped-space in that pool and if it finds enough of it, you will get a new logical volume that behaves more or less like a regular partition.
But LVM also offers you:
* RAID
* hot add/remove of physical volumes (drives backing it)
* hot add/remove/resize of logical volumes (directly usable slices of block device)
* thin volumes
* snapshots
* AFAIR storage replication via log shipping
* other funny targets like cache.

Things you CAN'T do with LVM:
* boot from it. (rumour says GRUB2 can. I never bother to check it because I like grub legacy and I simply have separate /boot)
* have root on LVM without initramfs. Genkernel supports it very well though.

Check LVM manual (or guides) for details. I've never done caching with LVM myself so I can't help you much more with setting it up. And I'm not sure this actually is what you're looking for, but it looks promising enough to try it.
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