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anguish anguish is offline
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Default Partition Alignment - Quick and Dumb Question - 05-15-2009, 11:59 AM

I haven't actually searched yet, but I'm just looking for a quick sentence or two on what it is. It apparently only has to do with SSD's, but that's about all I know.

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MoInSTL MoInSTL is offline
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Default 05-15-2009, 12:09 PM

It's supposed to improve disk performance. Several threads about it.


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Default 05-15-2009, 12:26 PM

Yeah, I caught that. I guess maybe what I'm looking for is why it's necessary? Or what exactly it even is.. Knowing there are several threads, any in particular that would explain it the best?


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Default 05-15-2009, 01:07 PM



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anguish anguish is offline
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Default 05-15-2009, 01:11 PM

Funny, I thought I just looked at that thread.. I must have missed where it got into some of the details on why it's necessary, and why, for example, a platter-based drive doesn't need it. I'll re-read it though.

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Default 05-15-2009, 02:49 PM

Quote:
Originally Posted by anguish View Post
Funny, I thought I just looked at that thread.. I must have missed where it got into some of the details on why it's necessary, and why, for example, a platter-based drive doesn't need it. I'll re-read it though.

Thanks!
Flash memory is read and written in blocks much larger that 512 byte sectors. Wikipedia has some more info. So, if your partitions aren't aligned to the flash memory's blocks, then many reads and writes will spill over into adjacent blocks, requiring more I/O.

And I've actually read that partition alignment can help on standard hard drives, because some actually manipulate data in 4KiB blocks, not 512byte sectors.


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mfruit mfruit is offline
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Default 05-18-2009, 08:33 PM

What I'm curious about is if 4K block alignment (64 sectors) is the universal magic number to use. That OCZ link says 128 sectors instead but from what I can tell, the various partitioning tools (Disk Utility, diskpart, etc.) default to 64 sectors.
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Default 05-20-2009, 12:55 AM

As long as it is not 63 (Windows XP Default) you should be okay. Some people recommend 64 others say 128. I have even seen people do 256. I did 64 and my Mini is running very well.

If you wanna be 100% sure do 128, but it shouldn't be needed.
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Default 05-20-2009, 01:25 AM

Quote:
Originally Posted by mfruit View Post
What I'm curious about is if 4K block alignment (64 sectors) is the universal magic number to use. That OCZ link says 128 sectors instead but from what I can tell, the various partitioning tools (Disk Utility, diskpart, etc.) default to 64 sectors.
If you setup your filesystem to use 4KiB blocks, which are common, I think there's little benefit to aligning on larger intervals than 4KiB.

Now, I've aligned my SSD to 512KiB, but I'm using the Ext4 filesystem and a alignment feature intended for RAID.

Also, your math is off. It's 2 sectors per KiB, so 64 sectors is 32KiB, 128 is 64KiB, etc.


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mfruit mfruit is offline
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Default 05-21-2009, 05:47 PM

How about multiple partitions? What's the best way to ensure that all of your partitions are properly aligned?

My SSD is configured like this:

Partition 1:
First 64
Last 26635769
Total 26635706

Partition 2:
First 26635770
Last 60179489
Total 33543720

Partition 1 is aligned but after doing some quick math, it doesn't seem like partition 2 is aligned.

Thanks.
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