From mboxrd@z Thu Jan 1 00:00:00 1970 From: Roberto Spadim Subject: Re: SSD - TRIM command Date: Wed, 9 Feb 2011 16:30:15 -0200 Message-ID: References: <4D517F4F.4060003@gmail.com> <4D5245DF.4020401@hardwarefreak.com> <20110209161916.GB8632@bounceswoosh.org> <20110209171744.GC8632@bounceswoosh.org> <20110209182426.GA2724@lazy.lzy> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20110209182426.GA2724@lazy.lzy> Sender: linux-raid-owner@vger.kernel.org To: Piergiorgio Sartor Cc: "Eric D. Mudama" , "Scott E. Armitage" , David Brown , linux-raid@vger.kernel.org List-Id: linux-raid.ids nice =3D) but check that parity block is a raid information, not a filesystem inf= ormation for raid we could implement trim when possible (like swap) and implement a trim that we receive from filesystem, and send to all disks (if it=B4s a raid1 with mirrors, we should sent to all mirrors) i don=B4t know what trim do very well, but i think it=B4s a very big wr= ite with only some bits for example: set sector1=3D'00000000000000000000000000000000000000000000000000' could be replace by: trim sector1 it=B4s faster for sata communication, and it=B4s a good information for hard disk (it can put a single '0' at the start of the sector and know that all sector is 0, if it try to read any information it can use internal memory (don=B4t read hard disk), if a write is done it should write 0000 to bits, and after after the write operation, but it=B4s internal function of hard disk/ssd, not a problem of md raid... md raid should need know how to optimize and use it =3D] ) 2011/2/9 Piergiorgio Sartor : >> ext4 send trim commands to device (disk/md raid/nbd) >> kernel swap send this commands (when possible) to device too >> for internal raid5 parity disk this could be done by md, for data >> disks this should be done by ext4 > > That's an interesting point. > > On which basis should a parity "block" get a TRIM? > > If you ask me, I think the complete TRIM story is, at > best, a temporary patch. > > IMHO the wear levelling should be handled by the filesystem > and, with awarness of this, by the underlining device drivers. > Reason is that the FS knows better what's going on with the > blocks and what will happen. > > bye, > > pg > >> >> the other question... about resync with only write what is different >> this is very good since write and read speed can be different for ss= d >> (hd don=B4t have this 'problem') >> but i=B4m sure that just write what is diff is better than write all >> (ssd life will be bigger, hd maybe... i think that will be bigger to= o) >> >> >> 2011/2/9 Eric D. Mudama : >> > On Wed, Feb =A09 at 11:28, Scott E. Armitage wrote: >> >> >> >> Who sends this command? If md can assume that determinate mode is >> >> always set, then RAID 1 at least would remain consistent. For RAI= D 5, >> >> consistency of the parity information depends on the determinate >> >> pattern used and the number of disks. If you used determinate >> >> all-zero, then parity information would always be consistent, but= this >> >> is probably not preferable since every TRIM command would incur a= n >> >> extra write for each bit in each page of the block. >> > >> > True, and there are several solutions. =A0Maybe track space used v= ia >> > some mechanism, such that when you trim you're only trimming the >> > entire stripe width so no parity is required for the trimmed regio= ns. >> > Or, trust the drive's wear leveling and endurance rating, combined >> > with SMART data, to indicate when you need to replace the device >> > preemptive to eventual failure. >> > >> > It's not an unsolvable issue. =A0If the RAID5 used distributed par= ity, >> > you could expect wear leveling to wear all the devices evenly, sin= ce >> > on average, the # of writes to all devices will be the same. =A0On= ly a >> > RAID4 setup would see a lopsided amount of writes to a single devi= ce. >> > >> > --eric >> > >> > -- >> > Eric D. Mudama >> > edmudama@bounceswoosh.org >> > >> > -- >> > To unsubscribe from this list: send the line "unsubscribe linux-ra= id" in >> > the body of a message to majordomo@vger.kernel.org >> > More majordomo info at =A0http://vger.kernel.org/majordomo-info.ht= ml >> > >> >> >> >> -- >> Roberto Spadim >> Spadim Technology / SPAEmpresarial >> -- >> 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 > > -- > > piergiorgio > -- > 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