Konstantin Sharlaimov <[EMAIL PROTECTED]> writes:
> On Wed, 2007-11-07 at 10:15 +0100, Goswin von Brederlow wrote:
>> I wonder if there shouldn't be a way to turn this off (or if there
>> already is one).
>>
>> Or more generaly an option to say what is "near". Specifically I would
>> like to teach the raid1 layer that I have 2 external raid boxes with a
>> 16k chunk size. So read/write within a 16k chunk will be the same disk
>> but the next 16k are a different disk and "near" doesn't apply
>> anymore.
>
> Currently there is no way to turn this feature off (this is only a
> "request for comments" patch), but I'm planning to make it configurable
> via sysfs and module parameters.
>
> Thanks for suggestion for the "near" definition. What do you think about
> adding the "chunk_size" parameter (with the default value of 1 chunk = 1
> sector). Setting it to 32 will make all reads within 16k chunk to be
> considered "near" (with zero distance) so they will go to the same disk.
>
> Max distance will also be configurable (after this distance the "read"
> operation is considered "far" and will go to randomly chosen disk)
>
> Regards,
> Konstantin
Maybe you need more parameter:
chunk_size - size of a continious chunk on the (multi disk) device
stripe_size - size of a stripe of chunks spanning all disks
rotation_size - size of multiple stripes before parity rotates to a
new disk (sign gives direction of rotation)
near_size - size that is considered to be near on a disk
I would give all sizes in blocks of 512 bytes or bytes.
Default would be:
chunk_size = 1 (block)
stripe_size = 1 (block)
rotation_size = 0 (no rotation)
near_size = 256
That would reflect that you have all chunks continious on a normal
disk and read/writes are done in 128K chunks.
For raid 1 on raid 0:
chunk_size = raid chunk size
stripe_size = num disks * chunk_size
rotation_size = 0
near_size = 256
For raid 1 on raid 5:
chunk_size = raid chunk size
stripe_size = (num disks - 1) * chunk_size
rotation_size = (num disks - 1) * chunk_size (?)
near_size = 256
and so on.
MfG
Goswin
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