[ale] OT: WD "Advanced Format" and "Green Drives"

[Greg Freemyer]

Michael,

I read through your stuff and the link you pointed at.

I saw no "end-user" benefits to a 4K sector drive that make me buy one today.

   (And I need to order some drives this afternoon by chance.)

It might be a little cheaper, but I just checked at Fry's online and found:

WD 1.5 TB drive with 4K sectors - $109
Seagate 1.5 TB drive (I think with 512 byte sectors) - $119

For me it is not worth $10 a drive to have to remember that I need to
align my partitions to 4K when I'm working with that WD.

Especially since that particular WD drive tells linux that it is a
512/512 drive instead of telling the truth and saying it is a 512/4096
drive.  I've seen complaints about it on the mdraid list and
elsewhere, but I don't know how the kernel team is going to address
it.  Maybe they are simply going to call it a WD bug and ignore it?

Greg

On Mon, Apr 12, 2010 at 9:32 AM, Michael Trausch <mike at trausch.us> wrote:
> On Mon, 2010-04-12 at 08:57 -0400, Greg Freemyer wrote:
>> On Fri, Apr 9, 2010 at 5:31 PM, Michael Trausch <mike at trausch.us> wrote:
>> > On Fri, 2010-04-09 at 13:45 -0400, Greg Freemyer wrote:
>> >> I would avoid drives with 4KiB physical blocks for a while longer
>> >> unless you want to take extra care about alignment etc.
>> >
>> > It should not be a great issue; the only thing that you have to be sure
>> > about is to align the start of a partition correctly.  The ext2/3/4
>> > family of filesystems already uses 4KiB blocks by default for many
>> > configurations, and so honestly the only real care that you have to take
>> > is to be sure that the start of the first 4KiB block is on a native
>> > boundary.
>>
>> Surprisingly some of the partitioning tools fail if you try to work
>> with partitions that don't follow their preconceptions about how the
>> start and end of partitions should align with cylinders.
>
> It's not (terribly) surprising, though if memory serves, you can tell
> the programs (at least fdisk and sfdisk) to ignore their notions and
> safety checks, and they will do so.  I'd need to read the man page to be
> sure, something which I have not yet had enough coffee to do.  :-)
>
>> sfdisk and cfdisk have neither been updated to be more flexible.
>
> cfdisk is pretty strict; it expects partitions to land on even
> boundaries, for example (which they should anyway).
>
>> Below is a cut and paste from a lkml email from just last week.  Note
>> the fatal error at the end.
>>
>> ===
>> I created this partition table using cfdisk (util-linux 2.17 from
>> debian/experimental). I guess even that is too old?
>>
>> I now re-created the partition table using fdisk from util-linux-ng
>> git and got this:
>>
>> Command (m for help): p
>>
>> Disk /dev/sdb: 2000.4 GB, 2000398934016 bytes
>> 81 heads, 63 sectors/track, 765633 cylinders, total 3907029168 sectors
>> Units = sectors of 1 * 512 = 512 bytes
>> Sector size (logical/physical): 512 bytes / 512 bytes
>> I/O size (minimum/optimal): 512 bytes / 512 bytes
>> Disk identifier: 0x2afff6d1
>>
>>   Device Boot      Start         End      Blocks   Id  System
>> /dev/sdb1            2048  3907029167  1953513560   83  Linux
>>
>> but:
>>
>>
>> $ sudo cfdisk -P s /dev/sdb
>> FATAL ERROR: Bad primary partition 0: Partition ends in the final
>> partial cylinder
>>
>> ===
>
> Yes, and that is wholly unsurprising.  cfdisk will make this complaint
> with any partition that has been created with a tool that lands a
> partition this way, though the reasons are mostly historical as I
> understand it.  cfdisk is designed to be more-or-less end-user facing.
> Had they used "cfdisk -z" and created a single partition, they would
> have gotten a partition that was properly constructed (that is, with the
> final sector on the last sector of the second-to-last cylinder on the
> disk).  Again, I don't recall _why_ that's the historic convention, but
> I _do_ recall that there was at least once upon a time a reason for it.
>
>> I'm not saying its real hard to work with 4K physical sector drives,
>> but it does introduce problems with little or no benefit.
>>
>> Or if there is benefit, what is it?
>
> AIUI, it has to do with "sector death".  That is, failure rates for
> sectors have stayed relatively constant, but (obviously) the number of
> sectors on-disk has grown over the past several years---leading to the
> same rates of failure on a sector-by-sector level, but higher rates of
> failure in terms of per disk.
>
> So, a drive with 4,096 byte sectors is going to have fewer sectors, but
> a relatively same-sized spare sector store (in terms of the number of
> sectors) and should be able to tolerate losing more bytes (though fewer
> sectors).  Since sector failures (at least in my experience) tend to
> have sequential runs to them, I imagine that this would have at least
> some benefit.
>
> There is also the idea that there will be more available storage given a
> platter that has the same number of bytes on it, because there is
> reduced overhead for things like per-sector data storage overhead on the
> platter.
>
> Here's one site that talks about it in a bit more detail:
>
>  http://www.anandtech.com/show/2888
>
> I read some other stuff "directly from the horse's mouth" some time
> back, but I cannot find the links.
>
>        --- Mike
>
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-- 
Greg Freemyer
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