Does anyone know if 4k sectors will be handled better by the kernel in Centos6? I'd like to copy backups to a 750Gb laptop type drive for offsite storage but the best write speed I can get is about 8MB/sec even with dd to the raw disk which shouldn't have an issue with partition alignment.
On 02/06/11 1:14 PM, Les Mikesell wrote:
Does anyone know if 4k sectors will be handled better by the kernel in Centos6? I'd like to copy backups to a 750Gb laptop type drive for offsite storage but the best write speed I can get is about 8MB/sec even with dd to the raw disk which shouldn't have an issue with partition alignment.
what are you using on dd as the blocksize (bs=) ? should be a fairly large multiple of 4K, like 1048576 (eg, 1MB writes).
I get 50-80MB/sec writes to a laptop drive hooked up to my windows desktop when I'm cloning said laptop drives. if you're only seeing 8MB, something is very wrong.
On 2/6/11 3:30 PM, John R Pierce wrote:
Does anyone know if 4k sectors will be handled better by the kernel in Centos6? I'd like to copy backups to a 750Gb laptop type drive for offsite storage but the best write speed I can get is about 8MB/sec even with dd to the raw disk which shouldn't have an issue with partition alignment.
what are you using on dd as the blocksize (bs=) ? should be a fairly large multiple of 4K, like 1048576 (eg, 1MB writes).
I get 50-80MB/sec writes to a laptop drive hooked up to my windows desktop when I'm cloning said laptop drives. if you're only seeing 8MB, something is very wrong.
Not all laptop drives use 4k sectors - probably just 750Gb and up.
I was using obs=4M. I thought there was more to it than alignment - and changes were made in more current kernels to help with the speed.
the best write speed I can get is about 8MB/sec
A while back I researched 4k sector drives since most new drives have them now. There is a problem with speed if you get the partition wrong.
The answer seems to be to creating a partition with 1 meg of unpartitioned space preceding the first partition. This causes sector 2048 to be the first sector of the partition, and avoids the problem.
Newer versions of gparted do this for you automatically when you use it to create a partition.
On Sun, Feb 6, 2011 at 4:50 PM, compdoc compdoc@hotrodpc.com wrote:
the best write speed I can get is about 8MB/sec
A while back I researched 4k sector drives since most new drives have them now. There is a problem with speed if you get the partition wrong.
The answer seems to be to creating a partition with 1 meg of unpartitioned space preceding the first partition. This causes sector 2048 to be the first sector of the partition, and avoids the problem.
Newer versions of gparted do this for you automatically when you use it to create a partition.
This turns out to also be a significant issue with RHEL/CentOS 5 and virtualized OS images, where the upstream repository has 4096 byte blocks, whether NetApp or some other architecture. NetApp images in VMWare get.... unhappy if you use the standard allocated 63 blocks for the BIOS and partition records. They're much, much happer if the begging of the first logical volume begins at block 65, but there's no graceful way to set this up in anaconda or most configuration tools. You have to pre-script it with parted.
On Sun, Feb 06, 2011 at 02:50:34PM -0700, compdoc wrote:
the best write speed I can get is about 8MB/sec
A while back I researched 4k sector drives since most new drives have them now. There is a problem with speed if you get the partition wrong.
The answer seems to be to creating a partition with 1 meg of unpartitioned space preceding the first partition. This causes sector 2048 to be the first sector of the partition, and avoids the problem.
Newer versions of gparted do this for you automatically when you use it to create a partition.
Just did a SL 6.0 install on a machine with two Hitachi 2TB drives with 4K sectors. parted warned me that the default values I'd chosen weren't optimal for the sector size and I adjusted manually.
Note that I set these drives up post-install -- no idea if Anaconda would have done the "right thing" or not.
Ray
Am 07.02.2011 04:51, schrieb Ray Van Dolson:
On Sun, Feb 06, 2011 at 02:50:34PM -0700, compdoc wrote:
the best write speed I can get is about 8MB/sec
A while back I researched 4k sector drives since most new drives have them now. There is a problem with speed if you get the partition wrong.
The answer seems to be to creating a partition with 1 meg of unpartitioned space preceding the first partition. This causes sector 2048 to be the first sector of the partition, and avoids the problem.
Newer versions of gparted do this for you automatically when you use it to create a partition.
Just did a SL 6.0 install on a machine with two Hitachi 2TB drives with 4K sectors. parted warned me that the default values I'd chosen weren't optimal for the sector size and I adjusted manually.
Note that I set these drives up post-install -- no idea if Anaconda would have done the "right thing" or not.
Ray
RHEL 6's anaconda auto-aligns properly by starting at sector 2048.
Alexander
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Alexander Dalloz -
compdoc -
John R Pierce -
Les Mikesell -
Nico Kadel-Garcia -
Ray Van Dolson