From mboxrd@z Thu Jan 1 00:00:00 1970 From: Roberto Spadim Subject: Re: Best way (only?) to setup SSD's for using TRIM Date: Mon, 29 Oct 2012 16:06:13 -0200 Message-ID: References: <508D808A.7040100@curtronics.com> <508E9289.5070904@curtronics.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Curt Blank Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids maybe you want a 'cache', there's bcache and others patchs to kernel that make harddisk 'hibrid' (ssd+hdd), it's nice and have a good future in my opnion, google it, and tell what you think 2012/10/29 Curt Blank > > Thanks. That made me think. Since as I said it's mainly going to contain > the Linux OS that lessens my concern because of the static nature of those > files. With the exception of /var/log and the MySQL DB's. /var/log files > are rotated on a 24 hour basis, kept, then gzip'd after 14 days then kept, > pretty much forever as long as space is available. MySQL DB's are mostly > insert with some updates with the exception of the ZoneMinder DB which is > mostly inserts and deletes continuously, majority of the data seldom lives > past a month or two. > > I can maybe see the need for TRIM on /var/log and maybe /mysql and > possibly /usr/local (which is it's own MP) where I do all my code > development. > > Like I said, I'm not against compiling a kernel I just really don't want > to have to do that every time the distribution updates and installs a new > one. > > So still looking for a way to use TRIM with RAID1 which gets me back to > the LVM option I heard might work? > > Also trying to find out if using my raid card might be the ticket but if > not then it have to be the kernel if I want TRIM. > > On Mon, 29 Oct 2012, Roberto Spadim wrote: > > > trim is used by file system to clean space to new files be writen, in other > > words, if you never need new space you won't need trim > > does your application a log like app? if yes trim is useless, the only use > > here is if you delete old log files and it normally is very rare, maybe > > once a month, maybe a week? > > > > if you need always delete files and write new ones, yes trim can help you > > but it will not save your life, it give more 'clean' space to garbage > > collect of ssd, and ssd don't reuse spaces with informations, it will use > > new ones, so in other words a trim help ssd to write faster and dont do > > (read-merge-write) > > vertex 4 have a good firmware, i used a vertex 2 some years ago without > > trim, and it runs nice with mysql in a generic aplication with delete > > update select, it execute >300iops very easly, and 300MB/s too, i didn't > > checked a slow don't after some time using it, so i don't see why trim > > could speed a lot my app, > > try, and say what you got, it's not unsafe, and sounds good, i don't know > > about suse kernel support, but it's not hard to compile a new kernel if you > > need it > > > > i used the vertex2 in raid1 configuration (it's better for many threads > > apps like mysql, but worst for stream application, for stream a raid10 or > > raid0 is better) > > > > > > 2012/10/29 Curtis J Blank > > > > > 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. > > > > > > [Had to resend, got rejected due to "reason: 550 5.7.1 Content-Policy > > > reject msg: The message contains HTML subpart, therefore we consider it > > > SPAM or Outlook Virus." from ThunderBird] > > > > > > > > > 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 > > > > > >> 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 > > >> More majordomo info at http://vger.kernel.org/majordomo-info.html > > >> > > > > > > > > > > > > -- > > > Roberto Spadim > > > > > > > > > > > > > > > > > > -- > > Roberto Spadim > > -- Roberto Spadim