can a wrong alignment cause a decrease in a hdd's life
arundel at freebsd.org
Mon Dec 19 23:43:10 UTC 2011
On Mon Dec 19 11, Jeremy Chadwick wrote:
> On Mon, Dec 19, 2011 at 10:56:33PM +0000, Alexander Best wrote:
> > On Mon Dec 19 11, Poul-Henning Kamp wrote:
> > > In message <20111219224700.GA75581 at freebsd.org>, Alexander Best writes:
> > > >On Mon Dec 19 11, Poul-Henning Kamp wrote:
> > > >> In message <20111219221617.GA70383 at freebsd.org>, Alexander Best writes:
> > > >>
> > > >> >ps: the hdd only gets mounted read-only!
> > > >>
> > > >> There is no known wear-effects in flash storage as long as you
> > > >> only read.
> > > >>
> > > >> You may need to do refresh-writes every 5-10 years to avoid
> > > >> tunnel-leakage bit errors, but most flash controllers use semi-long
> > > >> ECC syndromes and will do so on first bit that gives an read error.
> > > >
> > > >this is a regular hdd i believe -- no ssd. at least when i plug it into my
> > > >usb drive i hear the hdd spinning up and causing vibrations. i don't think
> > > >that would be the case with an ssd.
> > >
> > > Ahh, sorry, I don't know why I thought it was flash.
> > no problem. so will the improper alignment also not cause a life expectancy
> > shortage in case of a hdd (non-flash-based)?
> The improper alignment will result in sub-par write performance, and a
> slight decrease in read performance writes -- but will not impact life
> expectancy or "harm" the drive in any way.
> I recommend strongly that you rectify the situation before you get too
> carried away with software installations, etc..
> And yes I am aware what you have is a mechanical HDD not an SSD (I say
> in this advance of what I'm about to write).
> If you need a ""safe"" alignment value, most software on Windows
> (including Windows 7) pick a value of 2MBytes as the alignment offset,
> which I believe is LBA 4095, since everything software-wise uses
> 512-byte sectors. That's calculated via: 2097152 / 512.
> This number is also evenly divisible by 4096 bytes (which is what you're
> trying to ensure for performance).
> Readers, as well as you, may wonder where the "magical" 2MByte value
> comes from, and can you pick something smaller. Yes you can pick
> something smaller, but the value itself stems from the added complexity
> of SSDs and NAND erase page size vs. NAND page size. A value of 2MBytes
> works well on all brands of SSDs on the market (as of this writing).
> Which reminds me -- I need to go back and redo most of our systems that
> use Intel SSDs, since at the time I picked the default offset in
> sysinstall (LBA 63, thus 64 * 512 = 32KBytes), which though divisible by
> 4096, is not optimal for NAND erase page size.
> I would love to advocate FreeBSD change sysinstall/bsdinstall to use a
> default offset of 2MBytes, but I imagine that would upset a lot of
> people who install FreeBSD on "limited space" devices (CF, etc.).
> Honestly though, with the size of media these days........
thanks a lot for the explanation. i'm going to get another drive, soon, and
will then be able to "fix" the alignment, as i currently have no place where
i can backup the data of my current (misaligned) hdd.
> > and one other question: the hdd also supports usb 3. will the improper
> > alignment have any effect (speed wise) when connected via usb 3, or is even
> > usb 3 too slow to notice the performance drop due to the improper alignment?
> USB 3.0 vs. 2.0 vs. eSATA vs. native SATA has no bearing on the
> situation. Those are transport protocols that define "maximum
> By the way, the hard disk itself does not "support USB 3.0" -- your
> drive is in an enclosure that contains a SATA<->USB3.0 conversion
> chipset inside. If you open the enclosure, you will find the hard disk
> is SATA, and probably supports SATA600.
i was ware of this fact. what i meant by speed in connection with usb 3 was the
following example-case (please don't take the numbers literally)
1) the drive itself can do 500 mb/sec when aligned properly
2) the drive does 350 mb/sec when aligned improperly (512 boundry)
3) usb 3 can do 100 mb/sec
... so in this case the improper alignment wouldn't have an impact, since
even with proper alignment only 100 mb/sec were possible. however in the
1) 500 mb/sec
2) 100 mb/sec
3) 200 mb/sec
the improper alignment would have an impact, since usb 3 *could* perform at
200 mb/sec with proper alignment, but will drop to 100 mb/sec in the case of
again...please don't take the transfer rates literaly. they're most defenately
> | Jeremy Chadwick jdc at parodius.com |
> | Parodius Networking http://www.parodius.com/ |
> | UNIX Systems Administrator Mountain View, CA, US |
> | Making life hard for others since 1977. PGP 4BD6C0CB |
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