also sprach Boyd Stephen Smith Jr. <bss@iguanasuicide.net> [2010.06.15.2108 +0200]: > > Use mdadm for a RAID5 or RAID6 and LVM on top for the remaining > > cases when you need space and care less about performance. > > Use RAID 1/0 in mdadm when you need redundancy, space, and performance. > > (Although, IME, RAID 5 is not badly performing.) Sure it is, on writes. If you have the right hardware, you won't notice, but every write takes twice as much work. http://git.debian.org/?p=pkg-mdadm/mdadm.git;a=blob;f=docs/RAID5_versus_RAID10.txt;hb=refs/heads/contrib/docs/raid5-vs-raid10 > This is particularly useful when you have 3 disks, but only need one disk > redundancy. mdadm can layout data like this: > > | disk1 | disk2 | disk3 | > +-------+-------+-------+ > | dataA | dataA | dataB | > | dataB | dataC | dataC | > > LVM cannot, easily. > > RAID 1/0 through mdadm with 4 disks is also better than strictly layering the > RAID levels. Do you have any data to back this up? Fundamentally, the data will traverse one layer less, but does it actually make a difference? > mdadm 0/1 4 disk, 1 redundant copy of data: > | disk1 | disk2 | disk3 | disk4 | > +-------+-------+-------+-------+ > | dataA | dataA | dataB | dataB | > | dataC | dataD | dataC | dataD | > | dataE | dataF | dataF | dataE | > > (same redundancy level as RAID 5, no parity calculations needed.) > > mdadm 0/1 4 disk, 2 redundant copy of data: > | disk1 | disk2 | disk3 | disk4 | > +-------+-------+-------+-------+ > | dataA | dataA | dataA | dataB | > | dataB | dataB | dataC | dataC | > | dataC | dataD | dataD | dataD | > > (same redundancy level as RAID 6, although some capacity may be > lost near the end, no parity calculations needed.) More info (and patches welcome): http://git.debian.org/?p=pkg-mdadm/mdadm.git;a=blob;f=docs/RAID5_versus_RAID10.txt;hb=refs/heads/contrib/docs/raid5-vs-raid10 http://git.debian.org/?p=pkg-mdadm/mdadm.git;a=blob;f=debian/FAQ;hb=HEAD#l106 -- .''`. martin f. krafft <madduck@d.o> Related projects: : :' : proud Debian developer http://debiansystem.info `. `'` http://people.debian.org/~madduck http://vcs-pkg.org `- Debian - when you have better things to do than fixing systems "you don't sew with a fork, so I see no reason to eat with knitting needles." -- miss piggy, on eating chinese food
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