Comments on: Aligning SSD Partitions

By: Jeff Orrok

Jeff Orrok — Wed, 22 Feb 2012 20:49:46 +0000

time for another dumb question: if I use the graphical “disk utility” that comes with CentOS 6 and use the setting to align partitions by MiB, wouldn’t that take care of aligning things on the SSD and eliminate having to worry about all of the exotic geometry calculations?

By: Glottis

Glottis — Thu, 12 May 2011 07:38:30 +0000

I’m planning on building a system with an SSD for the OS (Ubuntu). Would it work if I first use FDISK on it as described and then let Ubuntu install? (And preferably without custom settings or would those undo the allignment I made with FDISK)?
Also, could you maybe comment on eekamran’s comment about the SSD’s controller making these instructions unnecessary? (At least that’s what I think he’s saying).
Thank you (I’m a newbie).

By: rom828

rom828 — Mon, 02 May 2011 14:04:12 +0000

If I take 4 SSD disks and stripe them with RAID0 will the disks be aligned? I keep my OS on sda1, but build a RAID for scratch I/O with:

mdadm –create –verbose /dev/md0 –level=raid0 –raid-devices=4 /dev/sdb1 /dev/sdc1 /dev/sdd1 /dev/sde1

Each file system sdb1 .. sde1 were just created starting at the first cylinder.

By: eekamran

eekamran — Thu, 14 Apr 2011 11:54:31 +0000

I dont agree at all. In SSD there is a controller which is doing wear levelling and a FTL flash translation layer work in which the logical address from file system map to physical address of SSD. Its an illusion for filesystem. The actual phtsical memory of SSD is usually greator than logical memory as the FTL algo needs more space to do wear levelling.

By: Bryan Richard

Bryan Richard — Tue, 05 Apr 2011 17:34:46 +0000

Thanks for the heads-up @cibwaknoy. We updated the link.

By: cibwaknoy

cibwaknoy — Tue, 05 Apr 2011 14:45:57 +0000

Ted T'so's blog has moved. The SSD post is now at http://tytso.livejournal.com/2009/02/20/.

By: mwduffy

mwduffy — Tue, 29 Mar 2011 15:11:01 +0000

The article makes a small transposition error. It states “Using 56 sectors per track gives 56*512 bytes or 28,762 bytes per track.” My calculator disagrees: 56*512=28672.

Wouldn’t we all be better off if fdisk just used hex?

By: Jeffrey Layton

Jeffrey Layton — Mon, 28 Mar 2011 13:29:58 +0000

It’s funny but erases are still based on blocks. The basis for this is in the chip design (which I don’t know anything about). It seems like chips could be redesigned but I think this will also cause a big ripple in the whole design of the SSD.

I think the only way to get SSDs that have unlimited write cycles is to change the underlying technology. Not sure what it will be but I think you have to get away from the NAND tunneling concepts.

Jeff

By: ahaveland

ahaveland — Wed, 23 Mar 2011 12:02:36 +0000

Informative video, but surely when updating a bit, the level of granularity is a page and not a block of them?
Writing 512kb instead of a 4k page to change one bit seems really crazy to me.

(I’m still waiting for SSDs that have unlimited write cycles and none of this wear levelling stuff).

By: Jeffrey Layton

Jeffrey Layton — Mon, 21 Mar 2011 17:19:05 +0000

Oh boy do I owe @josir an apology. I meant to say that was NOT a dumb question. I didn’t check my response before I posted.

Once again – my apologies to josir. Your question was definitely not dumb – it was an excellent question.

Jeff

By: Jeffrey Layton

Jeffrey Layton — Sun, 20 Mar 2011 14:02:01 +0000

@josir,

It should apply to pen drives as well since they are constructed in the same manner. But pen drives are fairly slow sometimes because of the drive and sometimes because of the interface (e.g. USB). However, since they are built in the same way, it’s always worth trying (never hurts).

Good luck! (and that was a dumb question).

Jeff

By: josir

josir — Sun, 20 Mar 2011 11:34:13 +0000

Sorry if my question is dummy but is this rules also applies to Pen Drives?

By: Jeffrey Layton

Jeffrey Layton — Thu, 17 Mar 2011 17:22:16 +0000

@mbergandi,

I explicitly say that if you don’t partition on page boundaries you can get a performance hit because of pages going across block boundaries.

Jeff

By: Michael Bergandi

Michael Bergandi — Thu, 17 Mar 2011 15:18:40 +0000

In the video, Jeff states that it is the blocks that get rewritten and that there is a performance hit for having to writes crossing the block boundary, then goes on to try to align on a page…. huh? If you page align (not on a block boundary), then it seems to me that there is a much higher probability of having a multi-page write that will cross the block boundary, than if you were block aligned.

I think OCZ got it right.

By: zwoop

zwoop — Thu, 17 Mar 2011 14:41:26 +0000

As a side note, if you use the entire SDD for one file system (e.g. use /dev/sda instead of /dev/sd1), you obviously don’t need to partition the disk. And Since /dev/sda is aligned by definition, you don’t have to worry about any of this. This is generally not an option for a boot disk, but if you have one SSD dedicated for /home, by all means use the entire disk, and don’t worry about the magic numbers.