Re: RAID 6 mdadm
On 4/10/2013 12:32 PM, Dexter Filmore wrote:
> Am Wednesday 10 April 2013 18:05:08 schrieb Ross Boylan:
>>>
>>> You cannot get more than about 200MB/s out of a RAID1 setup, not even
>>> with
>>> 15krpm SAS drives. the RAID1 will never be faster than a single disk.
>>> How
>>> would it.
>>
>> It can read faster than a single disk by combining reads from different
>> sectors on different disks. I think your assertion is incorrect for
>> reading, though not for writing.
>>
>> Ross Boylan
>
> Then dm would have to manage/combine the reads from the involved disks.
> I do not know better, but I doubt this is done.
> I'll ask the raid list for curiousity's sake.
It's not necessary to ask on linux-raid, and as you have not yet done
so, I'll clarify this now:
Both the md RAID1 and RAID10 personalities will read sectors in parallel
from both disks in a mirror pair in most circumstances. This has been
the case for many years. This is a read optimization only. Writes
occur in parallel as well, obviously, but as it's the same data the net
data throughput isn't doubled, only the raw device throughput. This
should be obvious to anyone. I'm merely being complete in my description.
--
Stan
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