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Trying again. SSD + HDD + LVM? How would you install this?
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1clue
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PostPosted: Sat Oct 20, 2012 12:23 am    Post subject: Trying again. SSD + HDD + LVM? How would you install this? Reply with quote

Hi,

I recently tried to install Gentoo after a significant vacation in another distro. I failed miserably, never got it to boot on its own. I'd like to figure out what happened before I try again.

If you have a minute and some knowledge, please take some time to help me out.

Here's the interesting hardware:

  1. Intel i7 920 on an Asus P6T motherboard.
  2. 12g RAM.
  3. 1x240g SSD
  4. 1x750g HDD


I've installed Gentoo on this box several times, including both RAID and LVM2. I bought the hardware basically to play with distros on, so it's seen its share of distros. :)

What has changed since last time Gentoo was successfully installed is the SSD. I've never had one, don't particularly understand the strategy for installing on one, other than you want to keep the frequently written stuff off it and you want noatime.

Here's what I had planned last time:

  1. LVM2 for both volumes, including / but not of course /boot or swap
  2. /home, /var, other frequently written directories on HDD.
  3. / and mostly read-only directories on SSD.
  4. /var/tmp, /tmp and such on TMPFS


At the time, there was some sort of a warning that if you have /usr on a separate partition we needed an initramfs in order to mount it. And something about LVM2 needing to be on there too. I never figured out how to do initramfs. Yes I found the HOWTO but never made it work.

Historically speaking I've always been inclined to have a bunch of filesystems using LVM so I can grow them as appropriate.

If anyone has experience with SSDs and HDDs in combination, please let me know a strategy that works.

Thanks.
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NeddySeagoon
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PostPosted: Sat Oct 20, 2012 11:29 am    Post subject: Reply with quote

1clue,

First off, lifetime and wear levelling on newer SSDs is much better than the early ones where anacdoteal evidence suggests that you could kill the SSD by attempting to install Gentoo.

On the SSD you need a filesystem that supports trim as well as the noatime option.
trim erases the bocks occupied by a file as soon at it is deleted, so you don't wait the erase time when you come to reuse previously used blocks on the SSD.
Unlike a 'spinny' a SSD has separate erase and wire operations and erase is very slow.
The down side is that on an SSD using trim, you cannot recover files you deleted accidently.

You will need an initrd if you separate /var or /usr (or both) from root as udev demands that they be mounted before it starts.
The alternative is to use a forked udev. See the Announce: just another one udev fork
You also need an initrd if / (root) will be inside LVM.
You can get some hints on initrds here.

Why would you not put swap in LVM?

If you board is EFI and you plan to use EFI there are a few more complications.
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NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.
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d2_racing
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PostPosted: Sat Oct 20, 2012 11:41 am    Post subject: Reply with quote

Yeah, about the EFI stuff, I own a an Intel motherboard : http://www.intel.com/content/www/us/en/motherboards/desktop-motherboards/desktop-board-dz77bh-55k.html

That thing is all about UEFI, but it still can boot in Legacy-mode. So basically I was able to install my Gentoo box the old school way.

Maybe in a couple of months, the legacy stuff will me dropped, but as least I was lucky this time.

Finally, I own two Intel SSD 520 serie (240 and 120 gigs) and I use btrfs on those, because of the SSD,trim feature that Btrfs support.

With Btrfs you need to backup your stuff like any other filesystem and you will be good to go.
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1clue
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PostPosted: Thu Oct 25, 2012 12:43 pm    Post subject: Reply with quote

Thanks for your input, the world intervened yet again and so there will be more delay before getting started.

Thanks.
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