On 21/06/2011 12:42, NeilBrown wrote:
On Tue, 21 Jun 2011 11:56:41 +0100 Jonathan Tripathy<jonnyt@xxxxxxxxxxx>
wrote:
On 21/06/2011 11:45, NeilBrown wrote:
On Tue, 21 Jun 2011 11:24:20 +0100 Jonathan Tripathy<jonnyt@xxxxxxxxxxx>
wrote:
Hi Everyone,
Use md's "single process" RAID10 with the standard near layout (which is
apperently the same as RAID1+0 in industry), which 2 drives could fail
without loosing the array?
This is what I have:
Number Major Minor RaidDevice State
0 8 5 0 active sync /dev/sda5
1 8 21 1 active sync /dev/sdb5
2 8 37 2 active sync /dev/sdc5
3 8 53 3 active sync /dev/sdd5
Thanks
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Run
man 4 md
search for "RAID10"
read what you find, and if it doesn't make sense, ask again.
If it does make sense, post your answer and feel free to ask for
confirmation.
NeilBrown
Sorry, it still doesn't make much sense to me I'm afraid.
In fact, it's confused me more - since I'm using "near", does that means
that the "copy" (I'm using near=2) of a given trunk may lie on the same
disk, leading to *no redundancy*??
Clearly I need to improve the man page... (suggestions welcome).
How do you read it that the copies of a given chunk may lie on the same disk.
I read:
When 'near' replicas are chosen, the multiple copies of a given chunk
are laid out consecutively across the stripes of the array, so the two
copies of a datablock will likely be at the same offset on two adjacent
devices.
"laid out consecutively across the stripes of the array" might be a bit
obscure.. A stripe is one chunk on each device, so when chunks a laid out
consecutively across a stripe, they would be one chunk per device.
Then "likely be at the same offset on two adjacent devices" should make this
clearer. It is only "likely" because if you have an odd number of devices,
then the 2 copies of one chunk could be
a/ at offset X on the last device
b/ at offset X+chunk on the first device
but in general, they are on "adjacent devices"
So in answer to your original question, sda5 and sdb5 will have the same
data, and sdc5 and sdd5 will also have the same data.
NeilBrown
Hi Neil,
It was the lines in the "far" sections that made me have my doubts:
"When âfarâ replicas are chosen, the multiple copies of a
given chunk are laid out quite distant from each other. The
first copy of all data blocks will be striped across the early
part of all drives in RAID0 fashion, and then the next copy
of all blocks will be striped across a later section of all
drives, *always ensuring that all copies of any given block are
on different drives.*"
The highlighted part made me think that there would be a chance that
chunks would be on the same drive in near
Thanks
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