[arch-general] GPT slower than MBR, although both are properly aligned?
karol at babioch.de
Sat Jan 22 14:51:23 EST 2011
I'm about to setup a new Arch box and wanted to use GPT instead of the
(old) MBR partition scheme, just for the fun of it ;).
I've read through the various articles in the wiki, but it seems that
something strange is going on here.
I'm about to install the system to a SSD (Kingston S100), therefore I
also have to consider proper alignment. I've created the partition
scheme with gdisk (alignment set to 2048 boundary, although I've tried
it with different values (up to 8192), too), which basically looks like
Number Start (sector) End (sector) Size Code Name
1 2048 264191 128.0 MiB 0700 Linux/Windows data
2 264192 31277198 14.8 GiB 0700 Linux/Windows data
Take a look at the start sectors, they should be properly aligned to
2048, as 264192 is dividable by 2048.
In order to check the proper alignment I've run hdparm -tT over both
partitions, here are the results:
Timing cached reads: 12026 MB in 2.00 seconds = 6017.15 MB/sec
Timing buffered disk reads: 128 MB in 0.64 seconds = 201.56 MB/sec
Timing cached reads: 12086 MB in 2.00 seconds = 6047.19 MB/sec
Timing buffered disk reads: 278 MB in 3.02 seconds = 92.02 MB/sec
Quite a huge discrepancy considering the fact that a SSD should have
roughly the same speed everywhere.
Well, after fiddling around with it a little bit, I've finally tried the
same setup with the old MBR partition scheme, using fdisk, which gave me
the following partition scheme:
Device Boot Start End Blocks Id System
/dev/sda1 2048 264191 131072 83 Linux
/dev/sda2 264192 31277231 15506520 83 Linux
So the partition scheme is the same, despite the fact that the second
partition is a little bit bigger with MBR as there is no copy of the
With the MBR partitions I get the following results using hdparm -tT in
order to measure the speed:
Timing cached reads: 11578 MB in 2.00 seconds = 5793.15 MB/sec
Timing buffered disk reads: 128 MB in 0.63 seconds = 202.22 MB/sec
Timing cached reads: 11896 MB in 2.00 seconds = 5952.79 MB/sec
Timing buffered disk reads: 604 MB in 3.00 seconds = 201.16 MB/sec
So, both partitions are, as to be expected, equal in speed.
I'm quite astonished by these results, which confuse me totally. Is it
possible that GPT is slower than MBR? Is there something wrong
implemented within gdisk? Is there any explanation to that?
Right now the only thing I can do to get full speed is to use MBR once
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