From mboxrd@z Thu Jan 1 00:00:00 1970 From: Roberto Spadim Subject: Re: SSD - TRIM command Date: Wed, 9 Feb 2011 12:39:44 -0200 Message-ID: References: <4D517F4F.4060003@gmail.com> <4D5245DF.4020401@hardwarefreak.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: David Brown Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids guys... if my ssd fail, i buy another... let's make software ok, the hardware is another problem raid1 should work with floppy disks, hard disks, ssd, nbd... that's the= point make solutions for hardware mix the question is simple, could we send TRIM command to all mirrors (for stripe just disks that should receive it)? if device don't have TRIM we should translate it for a similar command, with the same READ effect (no problem if it's not atomic) the point of good read, i sent a email to maurice, and many others emails in this raid list, there's a new read balance mode for kernel 2.6.37 if you want try to benchmark it please test it: www.spadim.com.br/raid1 for me it's work very well with hd and ssd mixed array, i need more test and benchmark to neil accept it as a default feature of md the sysfs interface is poor yet, in future it should change the time based mode work, but it should have some features implemented in futures (queue time estimation) 2011/2/9 David Brown : > On 09/02/2011 08:44, Stan Hoeppner wrote: >> >> maurice put forth on 2/8/2011 11:37 AM: >>> >>> On 2/7/2011 1:07 PM, Roberto Spadim wrote: >>>> >>>> hi guys, could md send TRIM command to ssd? using ext4 discart >>>> mount option? if i mix ssd and hd, could this TRIM be rewrite to >>>> non TRIM compatible disks? >>>> >>> I have read that using md with SSDs is not a great idea: Form the >>> Fedora 14 documentation: >> >> Using any RAID level but pure striping with SSDs is a bad idea, for >> the exact reason in that documentation: =A0excessive writes. >> >> SSD - Solid State Drive >> >> Note the first two words. =A0Solid state device =3D integrated circu= it. >> ICs, including those comprised of flash memory transistors, have >> totally different failure modes than spinning rust disks, SRDs, or >> "plain old mechanical hard drives". >> >> RAID'ing SSDs with any data duplicative RAID level, any mirroring or >> parity RAID levels, _decreases_ the life of all SSDs in the array. >> This is the opposite effect of what you want: =A0reliability and >> lifespan. >> >> People have a misconception that SSDs are like hard disks. =A0The on= ly >> thing they have in common is that both store data and they can have = a >> similar interface (SATA). =A0The similarities end there. >> >> RAID is not a proper method of extending the life of SSD storage nor >> protecting the data on SSD devices. =A0If you want to pool all the >> capacity of multiple SSDs into a single logical device, use RAID 0 o= r >> spanning, _not_ a mirror or parity RAID level. =A0If you want to >> protect the data, snap it to a single large SATA drive, or a D2D >> backup array, and then to tape. >> > > First off, let me agree with you that backup is important no matter w= hat you > use as your primary storage. > > But beyond that, you've got a basic assumption wrong here. > > Good quality, modern SSDs do not have write-endurance issues. =A0It's= a thing > of the past. =A0Internally, of course, the flash /does/ have enduranc= e limits. > =A0But these are high (especially with SLC devices rather than MLC de= vices), > and the combination of ECC, wear-levelling and redundant blocks means= that > you can write to these devices continuously at high speed for /years/= before > endurance issues become visible by the host. =A0An additional effect = of the > extensive ECC is that undetected read errors are much less likely tha= n with > hard disks - when a failure /does/ occur, you know it has occurred. > > Many SSD models suffer from a certain amount of performance degradati= on when > they have been used for a while. =A0Intel's devices were notorious fo= r this, > though apparently they are better now. =A0But that's a speed issue, n= ot a > reliability or lifetime issue. > > SSDs (again, I refer to good quality modern devices - earlier models = had > more problems) are inherently more reliable than HDs, and have longer > expected lifetimes. =A0This means that it is often fine to put your S= SDs in a > RAID0 combination - you still have a greater reliability than you wou= ld with > a single HDD. > > However, SSDs are not infallible - using redundant RAID with SSDs is = a > perfectly valid setup. =A0Obviously you will have a whole disks worth= of extra > writes when you set up the RAID, and redundant writes means more writ= es, but > the SSDs will handle those writes perfectly well. > > > There is plenty of scope for md / SSD optimisation, however. =A0Good = TRIM > support is just one aspect. =A0Other points include matching stripe s= izes to > fit the geometry of the SSD, and taking advantage of the seek speeds = of SSD > (this is particularly important if you are mirroring an SSD and an HD= ). > > > -- > 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 =A0http://vger.kernel.org/majordomo-info.html > --=20 Roberto Spadim Spadim Technology / SPAEmpresarial -- To unsubscribe from this list: send the line "unsubscribe linux-raid" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html