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Would this work for soft Raid 10?
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dman777
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PostPosted: Tue Jan 04, 2011 5:58 am    Post subject: Would this work for soft Raid 10? Reply with quote

Would this work for soft Raid 10?

mdadm -C md0 -l=0 -d=2 /dev/sda1 /dev/sdb1
mdadm -C md1 -l=0 -d=2 /dev/sda2 /dev/sdb2

mdadm -C md2 -l=1 -d=2 /dev/md0 /dev/md1
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dmpogo
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PostPosted: Tue Jan 04, 2011 6:10 am    Post subject: Reply with quote

If anything, I would call it RAID 0+1 rather than RAID10

What is the point of this arrangement on two disks ?
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gentoo_ram
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PostPosted: Tue Jan 04, 2011 6:25 am    Post subject: Reply with quote

You have it backwards. You want to create 2 mirrorsets, they stripe them together. That way, if you lose a disk, you have less recovery. With the way you have it, if you lose a disk, you lose the other half of the stripe as well and are operating on only 2 disks.
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dman777
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PostPosted: Tue Jan 04, 2011 6:28 am    Post subject: Reply with quote

Woud haveing two mirrored sets and striping them together be slower?
New revised version:
mdadm -C md0 -l=1 -d=2 /dev/sda1 /dev/sdb1
mdadm -C md1 -l=1 -d=2 /dev/sda2 /dev/sdb2

mdadm -C md2 -l=0 -d=2 /dev/md0 /dev/md1

And what about this raid set up from the gentoo tutorial?
http://www.gentoo.org/doc/en/gentoo-x86+raid+lvm2-quickinstall.xml

What kind of benefits and drawbacks would come from this raid set up?
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ferg
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PostPosted: Tue Jan 04, 2011 9:39 am    Post subject: Reply with quote

Linux Raid10 is a special raid level that provides the striping and mirroring advantages of 0+1 in a single layer. It's different from Raid 1+0 and Raid 0+1 which are nested raid levels (i.e. a mirrored stripes or striped mirrors).

It's a pretty good raid level to choose for a Linux box. Easy to setup, pretty fast and fairly resilient.

http://en.wikipedia.org/wiki/Non-standard_RAID_levels#Linux_MD_RAID_10

BTW you can create a Raid10 array from two discs. Also using different partitions from the same disc does not add anything useful to an array. It does not increase resilience as if the disc goes both partitions are gone. It does not increase performance as heads cannot read from multiple partitions at the same time.
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gentoo_ram
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PostPosted: Tue Jan 04, 2011 5:41 pm    Post subject: Reply with quote

Oh yeah, I just noticed that. You really need 4 disks for a 0+1 setup or there's just no point. You don't get the performance advantage of 0+1 without at least 4 disks. If you only have 2 disks, then your choices are striping for pure performance or mirroring for redundancy (and some read performance increase).

0+1 can give better I/O performance than RAID 5, but at the cost of space efficiency. With 4 disks, 0+1 gives you a space efficiency of 50%. RAID5 on 4 disks will give you space efficiency of 75% with lower I/O performance. It all depends on what your goal is.
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