Tweaks for SSDs [Was: [gentoo-user] [ot] no more inodes]

[Florian Philipp]

Maxim Wexler schrieb:
> On 5/28/09, Volker Armin Hemmann <volkerarmin@××××××××××.com> wrote:
>> On Donnerstag 28 Mai 2009, Florian Philipp wrote:
>>> Maxim Wexler schrieb:
>>>> Hi group,
>>>>
>>>> For a netbook 4G SSD. Attempting to install mozilla-firefox. jdk
>>>> fails: No space left on device.
>>>>
>>>> df -i reveals no more inodes. I reboot thinking this will help. Wrong.
>>>> Lots of 'No space left on device messages'  with reference to
>>>> /var/lib/iinit.d/* in the boot console. And this gem: '*ERROR: local
>>>> is already starting'. And: '*ERROR: netmount is already starting'.
>>>>
[...]
>>>>
>>>> I know 4G is pretty small by today's standards but apart from xorg and
>>>> firefox everything else on this unit is command-line type utilities
>>>> and such. That can't account for 4G already.
>>>>
>>>> Maxim
>>> That you run out of inodes doesn't mean that you run out of physical (or
>>> logical) space on your disk. It just means that you run out of what you
>>> could call file descriptors.
>>>
>>> There is exactly one inode per file which stores meta information about
>>> this file. Ext2-4 have a fixed amount of inodes set when you format the
>>> partition. Reiserfs and JFS create them on the fly and therefore don't
>>> have problems with running out of inodes or wasting space on unused ones.
>>>
>>> Most likely you have a bunch of very small files on our disk, for
>>> example the portage tree. These don't consume much space but a lot of
>>> inodes.
>>>
>>> My advice: Save everything to another disk and then reformat the
>>> partition with a higher amount of inodes. If you use ext2, format it with
>>>
>>> mke2fs -N 732960 /dev/sda2
>>>
>>> This will create a file system with three times as many indoes as you
>>> had before.
>>>
>>> Hope this helps.
>> or don't use extX.
>>
>>
> Ok, thanks everybody, getting ready to dive in and fix this thing. Two
> more questions please:
>
[...]
>
> What's the best fs for a 4G SSD? I picked ext3 because of another eee
> forum post.
>
> Maxim
>

I just want to point to three blog posts from Theodore Ts'o:

Partioning scheme and formatting tricks for optimal performance:
http://thunk.org/tytso/blog/2009/02/20/aligning-filesystems-to-an-ssds-erase-block-size/

Talk about some general issues (ATA TRIM, mostly):
http://thunk.org/tytso/blog/2009/02/22/should-filesystems-be-optimized-for-ssds/

Making an argument for using journalling filesystems:
http://thunk.org/tytso/blog/2009/03/01/ssds-journaling-and-noatimerelatime/

Of course, T'so talks about an Intel X25-M which is a completely
different beast from those cheap SSDs you find in netbooks.

Delaying commits with ext4 and/or laptop-mode will reduce the wear-down
of your SSD but it might as well freeze your system when the actual
commit takes place because these things tend to have a terribly low
write performance.

In the end it will be a matter of playing with parameters.