[Discuss] ssd's in linux

[cra at WPI.EDU (Chuck Anderson)]

On Fri, Nov 08, 2013 at 06:15:32AM -0500, Stephen Adler wrote:
> I'm thinking of upgrading my linux system by adding an SSD drive to
> use as my system disk. Has anyone done this? Any pros and cons
> regarings using SSD's? I'm more intrested in the cons. I'm worried
> about the life expectancy since there is a limited number of writes
> one can do to the NAND memory. Do I need to setup a raid array to
> ensure the SSD contents are correct?

After trying out various methods of combining a SSD with a spinning
HDD (write-behind RAID etc.) I've settled on keeping the two drives
separate for performance reasons, and then using Lsyncd to synchronize
files between them in almost-realtime as an online backup.  Lsyncd
uses the inotify Linux kernel feature to determine what files/dirs
have changed in real time, and then it spawns rsync to do the actual
copies.

I partitioned the SSD and HDD identically, except for some extra space
on the SSD where I put a swap partition (yes I'm swapping to SSD but I
don't dip into swap much).  I also made sure to install the bootloader
on the HDD as well so I can boot from the HDD if the SSD dies.  Not
quite as resilient as RAID, but good enough for a desktop.

Just be sure to align your partitions (and any other block layers such
as LVM, LUKS, filesystems, etc.) to 2MiB boundaries for best SSD
performance and wear.  This should be the default for all modern
tools/distros these days.  You may also want to enable TRIM on the
SSD, although recent research brings into question the value of TRIM
and whether it actually hurts performance rather than helping it.

I'm just not going to be paranoid about wearing out the SSD,
especially since I have lsync there to keep my backups.  With the
whole system on SSD performance is outstanding.