On Wed, Feb 09, 2011 at 04:30:15PM -0200, Roberto Spadim wrote: > nice =) > but check that parity block is a raid information, not a filesystem information > 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´s a raid1 with mirrors, we should sent to all mirrors) To all disk also in case of RAID-5? What if the TRIM belongs only to a single SDD block belonging to a single chunk of a stripe? That is a *single* SSD of the RAID-5. Should md re-read the block and re-write (not TRIM) the parity? I think anything that has to do with checking & repairing must be carefully considered... bye, pg > i don´t know what trim do very well, but i think it´s a very big write > with only some bits for example: > set sector1='00000000000000000000000000000000000000000000000000' > could be replace by: > trim sector1 > it´s faster for sata communication, and it´s 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´t read hard disk), if a write is done it should > write 0000 to bits, and after after the write operation, but it´s > internal function of hard disk/ssd, not a problem of md raid... md > raid should need know how to optimize and use it =] ) > > 2011/2/9 Piergiorgio Sartor <piergiorgio.sartor@xxxxxxxx>: > >> 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 ssd > >> (hd don´t have this 'problem') > >> but i´m 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 too) > >> > >> > >> 2011/2/9 Eric D. Mudama <edmudama@xxxxxxxxxxxxxxxx>: > >> > On Wed, Feb 9 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 RAID 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 an > >> >> extra write for each bit in each page of the block. > >> > > >> > True, and there are several solutions. Maybe track space used via > >> > some mechanism, such that when you trim you're only trimming the > >> > entire stripe width so no parity is required for the trimmed regions. > >> > 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. If the RAID5 used distributed parity, > >> > you could expect wear leveling to wear all the devices evenly, since > >> > on average, the # of writes to all devices will be the same. Only a > >> > RAID4 setup would see a lopsided amount of writes to a single device. > >> > > >> > --eric > >> > > >> > -- > >> > Eric D. Mudama > >> > edmudama@xxxxxxxxxxxxxxxx > >> > > >> > -- > >> > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > >> > the body of a message to majordomo@xxxxxxxxxxxxxxx > >> > More majordomo info at http://vger.kernel.org/majordomo-info.html > >> > > >> > >> > >> > >> -- > >> Roberto Spadim > >> Spadim Technology / SPAEmpresarial > >> -- > >> To unsubscribe from this list: send the line "unsubscribe linux-raid" in > >> the body of a message to majordomo@xxxxxxxxxxxxxxx > >> More majordomo info at http://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@xxxxxxxxxxxxxxx > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > > > > > -- > Roberto Spadim > Spadim Technology / SPAEmpresarial > -- > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://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@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
