Re: [gentoo-user] SSD discard / fstrim
On Thursday 04 September 2014 11:57:19 Joseph wrote: This is my first SSD drive 480GB (the only one in the box). I read about all discard / trim option and just want to double check that I'm doing it correct. I setup standard Gentoo and per instruction in Handbook. Not I'm reading about discard http://wiki.gentoo.org/wiki/SSD Do I setup: fstrim -v / or discard in fstab: /dev/sda2 /boot ext2noauto,noatime 1 2 /dev/sda4 / ext4 defaults,relatime,discard 0 1 /dev/sda3 none swapsw,pri=3,discard0 0 Can I use them both? Do I need to add discard to /boot? Another possibility is to use f2fs (flash-friendly file system) rather than the usual Linux file-systems. Then trimming doesn't arise. http://git.kernel.org/?p=linux/kernel/git/jaegeuk/f2fs-tools.git;a=summary I have it on a little LAN server here and it seems to work just fine. Fit and forget. -- Regards Peter
Re: [gentoo-user] SSD discard / fstrim
On Thu, Sep 4, 2014 at 2:26 PM, Сергей protsero...@gmail.com wrote: You need to run Fstrim if you mounted your partition WITHOUT discard option and did lots of changes. For example, if you installed your system without discard, do fstrim and then add discard to /etc/fstab. Just a note that depending on the SSD model, discard can have a substantial performance penalty with negligible benefit compared to just sticking fstrim in your crontab. In theory the ssd should just handle discard by making a note of what is trimmed and utlizing this information when needed. In practice many ssds handle a trim by dropping whatever they're doing and don't a copy/delete cycle if only part of a block is trimmed, which defeats the whole point of trimming in the first place. FStrim has the advantage of being more asynchronous and possibly being able to consolidate trims over a longer time-period, which could improve performance if the ssd isn't smart about it. Is there a really good place to go for SSD reviews/etc that actually takes this sort of thing into account? After getting an SSD it became apparently that they vary widely in terms of quality. Heck, I can't even tell you what the erase cycle count is from the SMART info, while other models seems to provide all kinds of useful info. -- Rich
Re: [gentoo-user] SSD discard / fstrim
On 04/09/14 20:07, Rich Freeman wrote: On Thu, Sep 4, 2014 at 2:26 PM, Сергей protsero...@gmail.com wrote: You need to run Fstrim if you mounted your partition WITHOUT discard option and did lots of changes. For example, if you installed your system without discard, do fstrim and then add discard to /etc/fstab. Just a note that depending on the SSD model, discard can have a substantial performance penalty with negligible benefit compared to just sticking fstrim in your crontab. +1 also for lvm remember to add in lvm.conf issue_discards = 1 In theory the ssd should just handle discard by making a note of what is trimmed and utlizing this information when needed. In practice many ssds handle a trim by dropping whatever they're doing and don't a copy/delete cycle if only part of a block is trimmed, which defeats the whole point of trimming in the first place. FStrim has the advantage of being more asynchronous and possibly being able to consolidate trims over a longer time-period, which could improve performance if the ssd isn't smart about it. i understand that part of the reason it blocks so hard when run and hasn't been run is the ssd defrags/consolidates the used blocks too. it would be nice to know for sure what it's doing, or from kernel-space tell the ssd what is most likely to be changing and what can be consolidated happily. Is there a really good place to go for SSD reviews/etc that actually takes this sort of thing into account? After getting an SSD it became apparently that they vary widely in terms of quality. Heck, I can't even tell you what the erase cycle count is from the SMART info, while other models seems to provide all kinds of useful info. +1 for this as other factors such as the erase blocksize should be taken into account. i.e. the larger the erase blocksize the more need there is for fstrim in the first place, but also the filesystem/partition alignment becomes a magical dark art. -- Rich
