I am writing this because the stuff you need is not in one place elsewhere, this is what you really need to know, and i want to keep this very short, if you like you can read more elsewhere, this one will only share what you really should know.
1- Do i need trim ?
For reading NO, so if you write once and read 102112913 times, you are good without trimming anything, without trimming, disk writes are slow, reading is absolutely not affected by trim.
2- What is the difference between the ext4 discard option and running fstrim myself manually every once in a while, or even put it in a cron job ?
on ext4 with trim enabled, blocks are trimmed (erased) whenever they are no longer in use by the file system, meaning, when data is deleted from a block, the physical flash memory is erased right after the data deletion, so your disk will remain trimmed all the time, the overhead is not much because the OS knows the block it just freed, so it simply does no more math other than issue a second command to trim, when you run fstrim, fstrim will read the whole file system, and whenever it finds an empty spot, it will trim (hardware erase).
3- i forgot to enable discard, do i just enable it and all is good, is that safe.
Yes it is safe, but enable it, then manually run fstrim only once, or you can wait, and eventually all spots will be trimmed after the get written to and erased again.
Ext4 (the new linux file system) supports TRIM when you mount the disk with the discard option, you can use tools to trim with ext2 or ext3, but it won’t be automatic and not as efficient.
1- But i want ext2 because i don’t want Journaling
ext2 is in fact ext3 without the journal, in ext4 you can remove the journal as well with no problems at all, there are no consequences, ext4 was designed to run with or without journaling
How do i format the disk in ext 4 and enable trim ?
For instructions on creating ext4 partitions, see here , as for the mounting, the line should have an extra option called discard and it should look something like this in your /etc/fstab
UUID=b7a491b1-a690-468f-882f-fbb4ac0a3b53 /hds/3tb ext4 defaults,noatime,discard 0 1
You should be done, there is nothing more to do
3- I am stuck with ext2 and i don’t want to move, reformet and then move back again
before that, do you know that you can convert the drive to ext4 ?
4- I don’t want to convert anything to anything, i just want to manually trim
Thats easy, use the command
and you are done, but mind you, on anything but ext4, this will trim the whole unused space trimed or not trimmed