[CentOS] raid resync speed? - laptop drive-

[Les Mikesell]

On 5/26/2010 9:52 AM, John R Pierce wrote:
>
>>> Is that one of those WD drives that falsely
>>> reports its physical sector size as 512 bytes?
>>>
>>
>>  From the Scorpio blue specs, if I divide the capacity by the number of sectors, I get 512...
>>
>
>
>
> all these new 'advanced' drives look to the host like they have 512 byte
> sectors.... its just that they pack 8 of them internally into a single
> 4K sector.    if you don't ensure that your partitions start on a 4K (8
> sector) boundary, then committed random writes are very slow as your
> logical file system blocks will span multiple physical sectors

How can they ever be fast if the OS is writing 512 byte sectors?  The 
drive is going to have to read the 4k sector, merge the update, wait for 
the disk to spin around and write it back.  The read speed seems a match 
for a desktop Seagate with the same capacity, but writes are about 10x 
slower, even if I dd to the raw disk which should bypass any partition 
alignment issues.  And unfortunately since I want to store backups on 
it, the write speed is what matters.

-- 
   Les Mikesell
    lesmikesell at gmail.com