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 > bandwidth". > > 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 following example: 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 improper alignment. again...please don't take the transfer rates literaly. they're most defenately bogus. cheers. alex > > -- > | 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 |Received on Mon Dec 19 2011 - 22:43:10 UTC
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