Re: Best way (only?) to setup SSD's for using TRIM

[Curtis J Blank <curt@curtronics.com>]

Could you explain this a little more please? I don't understand why 
applications come into play? Thought the file system, in this case ext4, 
handles space allocation on the device not any application.

And here again, I don't need TRIM, but everything I've been reading, 
even from the SSD manufacturer, OCZ, says you do need TRIM to reduce 
write amplification.

If you don't need TRIM that makes things easy but my concern is write 
amplification over time.

[Geeze. Had to resend, twice now, evidently Robert's reply was in HTML 
"reason: 550 5.7.1 Content-Policy reject msg: The message contains HTML 
subpart, therefore we consider it SPAM or Outlook Virus." and 
ThunderBird even when set not to use HTML keeps it that way]

On 10/29/12 07:20, Roberto Spadim wrote:
> if you don't have DELETE and DROP in you application, you don't need
> TRIM...
>
> 2012/10/28 Curtis J Blank <curt@curtronics.com
> <mailto:curt@curtronics.com>>
>
>     I've got two new SSD's that I want to set up as RAID1 and use
>     strictly for the OS and MySQL DB's partitioned accordingly.
>
>     I'll be using the 3.4.6 kernel for now in openSuSE 12.2 with ext4.
>     So after a lot of Google'n and reading it is my understanding that
>     discard is not sent to the devices via the raid drivers. I am
>     aware of Shaohua Li's patches to make it work but am not inclined
>     to use them due to openSuSE's Online Update replacing the kernel.
>     I'm not against patching and gen'ing a kernel, that used to be
>     SOP, but just don't want deal with that overhead. Of course unless
>     I really need to.
>
>     So I've read, and if I understand things correctly, I can use LVM
>     and RAID1 and the the discard commands will be sent to the
>     devices. Is that correct and currently the only way or is/are
>     there other ways?
>
>     I've also read that a lot of people are saying TRIM isn't needed
>     because the SSD's garbage collection is so good now TRIM isn't
>     needed. But I don't see how that could work because the SSD's
>     don't have access to the file system so they don't know which
>     pages in the blocks are marked unused to do any consolidation and
>     erasing. And using TRIM is suggested in a OCZ document I read and
>     who's drives these are. Unless, the SDD when it has to change a
>     page moves the whole block then erases the old block? But without
>     TRIM in could be moving invalid data too because it doesn't know
>     that and that to me sure doesn't sound efficient and this
>     operation would be a perfect time to get rid of the invalid data
>     if it did know.
>
>     And due to PEC I'm wondering if this is even a good idea? Granted
>     the OS files can be considered somewhat static, with the exception
>     of /var/log so maybe that shouldn't go on the SSD, and maybe MySQL
>     shouldn't either because for things like ZoneMinder it's DB is
>     pretty dynamic. But with all the logging going on, and there is a
>     lot, and the dynamic nature of the MySQL data is the exact reason
>     I want it put it on SSD's, for the speed. See my quandary?
>
>     This is my best understanding of things right now so I came here
>     to and am asking the experts for help in clarifying and
>      understanding this and pick the best direction to go. Have the
>     SSD's for a couple of weeks now but holding off using them until
>     the I can determine the best way to use them. Oh and the SSD's are
>     OCZ Vertex 4 VTX4-25SAT3-256G.
>
>     Thanks.
>     --
>     To unsubscribe from this list: send the line "unsubscribe
>     linux-raid" in
>     the body of a message to majordomo@vger.kernel.org
>     <mailto:majordomo@vger.kernel.org>
>     More majordomo info at http://vger.kernel.org/majordomo-info.html
>
>
>
>
> --
> Roberto Spadim