The install handbook doesn't say anything about SSDs. This is unfortunate, as they are now very common, and users should do certain things differently for SSDs compared to HDDs. These "things" vary from the extremely important activating of TRIM features if using ext4 (mkfs.ext4 -E discard /dev/sdXY), to the less important but useful reducing swappiness (vm.swappiness=1 and vm.vfs_cache_pressure=50 to /etc/sysctl.conf) and I/O scheduler selection in the kernel.
Can you elaborate on the things we need to focus on? I don't have SDDs and have read contradictory posts about how Linux should be "tweaked" towards it.
TRIM with ext4: Enabling TRIM is very important. Paramount, in fact. The only filesystems I know that support it are btrfs and ext4. ext4 is very common, and does not enable TRIM per default. https://wiki.archlinux.org/index.php/Solid_State_Drives#Enable_TRIM_With_mkfs.ext4_or_tune2fs_.28Discouraged.29 Mount flags: Using noatime or relatime reduces write, and discard makes TRIM work. https://wiki.archlinux.org/index.php/Solid_State_Drives#Mount_Flags I/O scheduler: CFQ might not be optimal. In fact it almost definitely isn't. https://wiki.archlinux.org/index.php/Solid_State_Drives#I.2FO_Scheduler http://en.opensuse.org/SDB:SSD_performance#boot.local Increase time for dirty writeback etc: Less writing is good. I use the following, vm.swappiness=1 vm.vfs_cache_pressure=50 vm.dirty_writeback_centisecs=1500 vm.dirty_expire_centisecs = 500 vm.dirty_ratio=25 vm.dirty_background_ratio=10 other examples: http://en.opensuse.org/SDB:SSD_performance#boot.local Reduce swappiness: Less eager swapping means fewer writes. https://wiki.archlinux.org/index.php/Solid_State_Drives#Swap_Space_on_SSDs Compile in tmpfs: Writing to RAM doesn't hurt either. http://en.gentoo-wiki.com/wiki/Portage_TMPDIR_on_tmpfs NOTE that the article is maybe a bit outdated in some areas.
we should do something about this, indeed. i've written a few tips and tricks here and there, as i moved to using almost nothing but SSDs a few years ago, and i'm planning on building a new machine that will have only SSDs, using ext4. i thus have a vested interest, especially since i also need to find out what's needed to do a modern install on SSDs with newer filesystems, GPT partitioned, booting from UEFI motherboards, and all that jazz. if i can find the time, i can start a draft or somethin'.
(In reply to comment #3) > booting from UEFI motherboards http://blog.realcomputerguy.com/2012/05/efi-stub-booting-without-bootloader.html
I added in the discard mount option for SSD users. The CFQ issue is no longer prevalent, CFQ detects if an SSD is used and modifies its behavior. vm.* sysctls I rather not touch in the handbook; these are performance optimizing settings which require some knowledge that users at this point in the handbook can not have. Also, it is not that mandatory during installation (can be handled post-install). Compilation in tmpfs is only possible for systems with ample memory, not something we require for Gentoo (and thus not to document in the handbook).
