Mailinglist Archive: opensuse (933 mails)

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Re: [opensuse] openSUSE on SSD?
  • From: "Brian K. White" <brian@xxxxxxxxx>
  • Date: Tue, 01 Jun 2010 14:41:48 -0400
  • Message-id: <4C05546C.2010104@xxxxxxxxx>
On 6/1/2010 3:06 AM, Hans Witvliet wrote:
On Tue, 2010-06-01 at 08:09 +0200, Roger Oberholtzer wrote:
On Mon, 2010-05-31 at 23:32 +0200, Hans Witvliet wrote:

What about this stuff about aligning the disk blocks on a 4k boundary to
match the physical disk access? If that is not done when the disk is
formatted, there could be a performance penalty. I did not think
openSUSE did this.

you see things in the wrong perspective, imho.

For ages we use 512 byte blocks.
If you start using larger blocks you might gain some speed, but it
doesn't mean there is a performance penalty when using 512 byte blocks.

When doing a 20GB read, l get:
20480000000 bytes (20 GB) copied, 124.208 s, 165 MB/s
just a bit (185MB/s) faster when doing smaller transfers.
Good enough for a simple firewall, for me atleast...

What should i gain with 4K blocks?
I think this is more intended for ordinary drives with rotating
platters...
hw

The badness probably has more to do with the erase block size in ssd's and the finite number of write-ops per block in ssd's.
If the ssd deals in 4k chunks, but you only want to modify a 512byte chunk, or even a misaligned 4k chunk, perhaps you are forcing the ssd internally to do several other things to do something with the other 3 x 512 bytes just to accomplish the outward result of modifying the 1 x 512 bytes you were interested in.
Whereas if you tell the OS/filesystem to deal in the same 4k chunks and properly aligned, then you remove all extra work the ssd must do, and you probably double the life of the ssd since there is finite number to times a given block can be written or erased, and you are no longer making the ssd do multiple writes to accomplish what looks like one write outwardly. Heck, without proper alignment you might end up making the ssd write over two 4k internal ssd blocks (consuming the finite supply of write ops) just to change 20 bytes if they are in a 512byte filesystem block which spans over a 4k internal ssd block boundary. That is causing both unnecessary io operations overhead, and halving or thirding the life of the ssd.

See: http://ldn.linuxfoundation.org/blog-entry/aligning-filesystems-ssd’s-erase-block-size <http://ldn.linuxfoundation.org/blog-entry/aligning-filesystems-ssd%E2%80%99s-erase-block-size>
including the several links within that article more than the article itself.

It is _never_ correct to dismiss technical issues without knowing what they are.
It is _especially_ never correct to counsel others to do so.

--
bkw

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