Re: Query regarding stripe management in linux md-raid

[Goswin von Brederlow <goswin-v-b@web.de>]

Kunal Kushwaha <kunal.kushwaha@gmail.com> writes:

> Hi Goswin,
>
> My understanding of chunk size is that,  it is minimum unit of data
> that is used for read/write.
> Chunk size defines, amount of data written on one disk after breaking
> it in equal no of chunks.
> Chunk size = Stripe size /  (disks in array - parity disks)
>
> so for raid 5, chunk_size = Stripe_Size / (total_disks -1)
> and for raid 6, chunk_size = Stripe_Size / total_disks -2)
>
> and parity is also written in terms of chunk size.
>
> Now considering a case where IO request came for complete 1 stripe, we
> need buffer, for 1 stripe, but since we allocated 1 page per chunk,
> instead of 64k buffer we have only 4k buffer, So how this is handled?

No. read/write are generaly handled on a page size level, which almost
always means 4k. If you think about it you can easily split a chunk
into 4k bits and handle each one independently.

MfG
        Goswin