Re: raid resync speed? - laptop drive-

[Robert Nichols <rnicholsNOSPAM@xxxxxxxxxxx>]

On 05/22/2010 07:39 PM, Robert Nichols wrote:
> On 05/22/2010 05:46 PM, Les Mikesell wrote:
>> Does the 4K sector size mean that the drive is going to read the 4K chunk then
>> merge in the 512 bytes you wrote, the wait for the sector come around again to
>> write it back?  I guess that could explain the 10x write speed difference
>> regardless of cylinder alignment.   Read speed doesn't seem that much different.
>
> Yes, that's exactly what it means.  Every unaligned write or write that is
> not a multiple of the 4KB sector size becomes a read-modify-write within the
> drive, and a 10X reduction in write throughput is typical.

I should add that the kernel normally will do I/O in multiples of its 4KB
(typical) page size where possible, but I have no idea whether any effort
is made to align those writes if the drive does not report a 4KB physical
sector size, or whether it even makes sense to try beyond what the
elevator algorithm does for coalescing sequential writes.

I don't currently have any of these "enhanced format" drives, nor am I
using RAID, so all I can report is the collected experience of others.

-- 
Bob Nichols     "NOSPAM" is really part of my email address.
                 Do NOT delete it.

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