hummm.... thinking again..... what´s the today raid1 problem? it´s based on minimal disk size for example... /dev/sda 1gb /dev/sdb 1tb we can have a 1gb raid only what you want is: 1tb raid0 with a automatic /dev/sda to /dev/sdb write could we call this raid0-cache? i think we could implement it in raid.... check this fuse (filesystem) implementation: http://www.furquim.org/chironfs/ it´s based on filesystem (ok it´s a raid1, not a cache like, but´s limited to max filesystem size, not the minimal filesystem size... ok it´s not secure to use it since small filesystem don´t have all information, but´s nice) anyone want to make raid0-cache implementation? 2011/1/19 Roberto Spadim <roberto@xxxxxxxxxxxxx>: > i think we could make it > but not a raid feature > a linux feature > for example > > we could get ramdisk, nbd (network block device), ssd, hd, scsi, raid > and select what is first cache, and what is real value > > after this device is created we could use it with raid... > > > but.... the problem persist > if we lost energy, we can´t confirm that ram memory is sync to disk, > just if we don´t use memory cache... in other words we will work with > the best cache disk speed) > > since ram can get 32GB on big home computer > and ssd can get 1terabyte on big home computer > and hdd can get more than 1terabyte on big home computer > > we just need time to sync 32GB from memory to ssd > what´s the ssd speed? 300mb/s? we need 106,6666666666667 seconds to > sync memory to ssd, can you buy a ups with 107 seconds of life with a > serial cable (usb maybe) that inform that we are without energy? > > > > > > 2011/1/19 Cory Coager <ccoager@xxxxxxxxx>: >> On Wed, Jan 19, 2011 at 02:44:31PM -0200, Roberto Spadim wrote: >>> yes, a jornaling but using ssd first and sata after >>> it?s not raid feature... >>> it?s per disk filesystem feature... >>> we could implement jornaling in raid too... >>> but?s more inteligent (easy) at application level (filesystem) >>> you could write first at network (if it?s faster than sata) and after >>> at sata (if it?s slower than network) >>> >>> it?s not a raid feature... it?s a per device feature got it? >>> maybe a device (not raid..) for a cache division on devices >>> for example >>> >>> >>> /dev/sda (sata 1terabyte 100mb/s) >>> /dev/sdb (ssd 1gigabyte 1000mb/s) >>> >>> /dev/cache_a (a mix of sata and ssd with sata size 1terabyte, and >>> mixed speed (memory, ssd, sata)) >>> >>> cache_a device should know that >>> early reads/write should be writen to sdb >>> time in time it should sync at sda >>> >>> the same happens with memory (ram memory) but it?s volatille (diferent >>> than ssd that?s not volatille) >>> >>> /dev/sdb should be sync >>> /dev/sda should be async (since /dev/sdb make it safe to use async) >>> >>> >>> that?s you intention? i don?t know if linux have it, anyone know? >> I would use a physical ramdisk over a ssd but thats besides the point. >> They are still disk drives to the OS. >> >> Yes, I guess it would be similar to journaling but done in RAID >> itself. I don't believe it exists yet, thats why I'm asking if >> we could add support for this? >> -- >> 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 > -- 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
