Stripe dirty bitmap

Stripe dirty bitmap

[Bill Davidsen]

Sure would be nice to have md track whole never written stripes, so 
creating an array didn't have to be done over a three day weekend. When 
any part of a virgin stripe was written it could then be initialized 
properly, and when a virgin stripe was read zeros could be returned 
without disk i/o. It doesn't matter that the reads are done in parallel, 
with modern disk the bus is the bottleneck. With eSATA arrays the bus is 
slow to start with, passing TB through it should be avoided if possible.

-- 
Bill Davidsen <davidsen@tmr.com>
  "We can't solve today's problems by using the same thinking we
   used in creating them." - Einstein

Re: Stripe dirty bitmap

[Neil Brown]

On Sun, 04 Jul 2010 20:26:40 -0400
Bill Davidsen <davidsen@tmr.com> wrote:

> Sure would be nice to have md track whole never written stripes, so 
> creating an array didn't have to be done over a three day weekend. When 
> any part of a virgin stripe was written it could then be initialized 
> properly, and when a virgin stripe was read zeros could be returned 
> without disk i/o. It doesn't matter that the reads are done in parallel, 
> with modern disk the bus is the bottleneck. With eSATA arrays the bus is 
> slow to start with, passing TB through it should be avoided if possible.
> 

Sure would.

NeilBrown

Re: Stripe dirty bitmap

[Bill Davidsen]

Neil Brown wrote:
> On Sun, 04 Jul 2010 20:26:40 -0400
> Bill Davidsen <davidsen@tmr.com> wrote:
>
>   
>> Sure would be nice to have md track whole never written stripes, so 
>> creating an array didn't have to be done over a three day weekend. When 
>> any part of a virgin stripe was written it could then be initialized 
>> properly, and when a virgin stripe was read zeros could be returned 
>> without disk i/o. It doesn't matter that the reads are done in parallel, 
>> with modern disk the bus is the bottleneck. With eSATA arrays the bus is 
>> slow to start with, passing TB through it should be avoided if possible.
>>
>>     
>
> Sure would.
>   

Have to have a copy on each drive, I think? Use a bit for a group of N 
stripes or one per stripe? Put N in the metadata?
I'd use stripe_cache_size, but that changes.
As disk gets cheap (1.5TB for $65 this weekend?) bus speed is being an 
issue, more so with software raid which does the io out of system memory.

-- 
Bill Davidsen <davidsen@tmr.com>
  "We can't solve today's problems by using the same thinking we
   used in creating them." - Einstein