the question is: how many mirrors you have? you don´t have a partial mirror (i didn´t found it on raid documentation yet), or you have a working mirror or you don´t have the mirror and must resync to have a running one raid10 = raid1 but the raid1 devices are raid0 if you put raid1 over raid0 or raid0 over raid1 is not a diference of security. just a diference of how many time i will wait to resync the raid1 mirror (a big raid0 you slower than smallers harddisks/ssd devices) the question again: how many mirrors you have? 2011/1/31 Keld Jørn Simonsen <keld@xxxxxxxxxx>: > Top-posting... > > How is the raid0+1 problem of only 33 % survival for 2 disk with RAID10? > > I know for RAID10,F2 the implementation in Linux MD is bad. > It is only 33 % survival, while it with a probably minor fix could be 66%. > > But how with RAID10,n2 and RAID10,o2? > > best regards > keld > > > On Mon, Jan 31, 2011 at 05:15:29PM -0200, Roberto Spadim wrote: >> ok, but lost of a disk = problem with hardware = big problems = mirror failed >> think about a 'disaster recover' system >> you can?t lost the main data (you MUST have one 'primary' data source) >> >> raid1 don?t have ecc or anyother 'paged' data recover solution (it >> have just all mirror resync) >> >> let?s get back a level... (inside hard disk) >> if your hard disk have 2 heads, you have a raid0 inside you disk (got >> the point?) >> using your math, you should consider head problem (since it make the >> real read of information) >> >> but at raid (1/0) software (firmware) level, you have devices (with >> out without heads, can be memory or anyother type of adresseable >> information souce, RAID0 = DEVICE for raid software/firmware, but you >> have A DEVICE) >> >> for raid 1 you have mirrors(a copy of one primary device) >> if software find 1bit of error inside this mirror(device), you lost >> the full mirror, 1bit of fail = mirror fail!!!!! it?s not more sync >> with the main(primary) data source!!!! >> >> got the problem? mirror will need a resync if any disk fail (check >> what fail make you mirror to fail, but i think linux raid1 mirror fail >> with any disk fail) >> >> if you have 4 mirrors you can loose 4 disks (1 disk fail = mirror >> fail, 2 disk fail = mirror fail, 3 disk fail = mirror fail, any device >> with fail inside a raid1 device will make the mirror to fail, got? you >> can have good and bad disks on raid0, but you will have a mirror >> failed if you have >=1 disk fail inside your raid0) >> >> got the point? >> what?s the probability of your mirror fail? >> if you use raid0 as mirror >> any disk of raid0 failed = mirror failed got? >> you can lose all raid0 but you have just 1 mirror failed! >> >> >> could i be more explicit? you can?t make probability using bit, you >> must make probability using mirror, since it?s you level of data >> consistency >> =] got? >> >> >> 2011/1/31 Denis <denismpa@xxxxxxxxx>: >> > 2011/1/31 Roberto Spadim <roberto@xxxxxxxxxxxxx>: >> >> i think that partial failure (raid0 fail) of a mirror, is a fail >> >> (since all mirror is repaired and resync) >> >> the security is, if you lose all mirrors you have a device >> >> so your 'secure' is the number of mirrors, not the number of disks ssd >> >> or another type of device... >> >> how many mirrors you have here: >> >> raid0= 1,2(a) 3,4(b) >> >> raid1=a,b >> >> 1 mirror (a or b) >> >> >> >> and here: >> >> raid1=1,2(a) 3,4(b) >> >> raid0=ab >> >> 1 mirror (a or b) >> >> >> >> let?s think about hard disk? >> >> your hard disk have 2 disks? >> >> why not make two partition? first partition is disk1, second partition is disk2 >> >> mirror it >> >> what?s your security? 1 mirror >> >> is it security? normaly when a harddisk crash all disks inside it >> >> crash but you is secury if only one internal disk fail... >> >> >> >> that?s the point, how many mirror? >> >> the point is >> >> with raid1+0 (raid10) we know that disks are fragments (raid1) >> >> with raid0+1 we know that disks are a big disk (raid0) >> >> the point is, we can?t allow that information stop, we need mirror to >> >> be secured (1 is good, 2 better, 3 really better, 4 5 6 7...) >> >> you can?t break mirror (not disk) to don?t break mirror have a second >> >> mirror (raid0 don?t help here! just raid1) >> >> >> >> with raid10 you will repair smal size of information (raid1), here >> >> sync will cost less time >> >> with raid01 you will repair big size of information (raid0), here >> >> sync will cost more time >> > >> > Roberto, to quite understend how better a raid 10 is over raid 01 you >> > need to take down into a mathematical level: >> > >> > once I had the same doubt: >> > >> > "The difference is that the chance of system failure with two drive >> > failures in a RAID 0+1 system with two sets of drives is (n/2)/(n - 1) >> > where n is the total number of drives in the system. The chance of >> > system failure in a RAID 1+0 system with two drives per mirror is 1/(n >> > - 1). So, for example, using a 8 drive system, the chance that losing >> > a second drive would bring down the RAID system is 4/7 with a RAID 0+1 >> > system and 1/7 with a RAID 1+0 system." >> > >> > >> > Another problem is that in the case of a failury of one disk ( in a >> > two sets case), in a raid01 you will loose redundancy for ALL your >> > data, while in a raid10 you will loose redundancy for 1/[(n/2 >> > -1)/(n/2)], in the same case 1/4 of your data set. >> > >> > And also, in a raid 10 you will have o re-mirror just one disk in the >> > case of a disk failure, in raid 01 you will have to re-mirror the >> > whole failed set. >> > >> > -- >> > Denis Anjos, >> > www.versatushpc.com.br >> > -- >> > 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 > -- > 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
