Disk alignment used to be rather trivial to figure out. All the tracks had the same number of sectors of the same size. Modern high density drives use variable numbers of sectors per track maintaining roughly the same bit density on the platter. They still report the old sizing information of cylinders, tracks, and sectors. Actual sector geometry varies depending on where on the disk it is being written.

Actual addressing is usually done in LBA (Logical Block Addressing) format. And really doesn't care about the disk geometry. Split I/Os are likely to be done by the disks control software. You may get split I/Os where you don't expect them, and not where you expect them.

Put those disks in a SAN and share them out, and the geometry gets hidden behind another layer of geometry. At that point I wouldn't even try to hazard a guess at which I/Os were split when. I would be more interested in the SANs view which will likely stripe the data in some size which is a power of 2, likely somewhere between 4Kb and 4Mb. I/O on these boundaries will be split across disks. You SAN administrator should be able to tell you the SAN allocation size. It the allocation size is small it might be an advantage to align your partitions and block sizes with that of the SAN.

I generally look at sar output to see if Disk I/O is getting to be a problem. You will see average queue size and service times increasing when you have an I/O problem. At that point you need to start looking at why I/O is a problem. With a SAN it could occur at a number of places. There are a variety of solutions. For virtual machines, I would lean to separate SAN disks for each machine. These can be allocated as raw disks to the virtual machines rather than one of the virtual disk in a file formats like VMDK.

Disk alignment used to be rather trivial to figure out. All the tracks had the same number of sectors of the same size. Modern high density drives use variable numbers of sectors per track maintaining roughly the same bit density on the platter. They still report the old sizing information of cylinders, tracks, and sectors. Actual sector geometry varies depending on where on the disk it is being written.

Actual addressing is usually done in LBA (Logical Block Addressing) format. And really doesn't care about the disk geometry. Split I/Os are likely to be done by the disks control software. You may get split I/Os where you don't expect them, and not where you expect them.

Put those disks in a SAN and share them out, and the geometry gets hidden behind another layer of geometry. At that point I wouldn't even try to hazard a guess at which I/Os were split when. I would be more interested in the SANs view which will likely stripe the data in some size which is a power of 2, likely somewhere between 4Kb and 4Mb. I/O on these boundaries will be split across disks. You SAN administrator should be able to tell you the SAN allocation size. It the allocation size is small it might be an advantage to align your partitions and block sizes with that of the SAN.

I generally look at sar output to see if Disk I/O is getting to be a problem. You will see average queue size and service times increasing when you have an I/O problem. At that point you need to start looking at why I/O is a problem. With a SAN it could occur at a number of places. There are a variety of solutions. For virtual machines, I would lean to separate SAN disks for each machine. These can be allocated as raw disks to the virtual machines rather than one of the virtual disk in a file formats like VMDK.

Disk alignment used to be rather trivail to figure out. All the tracks had the same number of sectors of the same size. Modern high density drives use variable numbers of sectors per track maintaining roughly the same bit density on the platter. They still report the old sizing information of cylinders, tracks, and sectors. Actual sector geometry varies depending on where on the disk it is being written.

Actual addressing is usually done in LBA (Logical Block Addressing) format. And really doesn't care about the disk geometry. Split I/Os are likely to be done by the disks control software. You may get split I/Os where you don't expect them, and not where you expect them.

Put those disks in a SAN and share them out, and the geometry gets hidden behind another layer of geometry. At that point I wouldn't even try to hazard a guess at which I/Os were split when. I would be more interested in the SANs view which will likely stripe the data in some size which is a power of 2, likely somewhere between 4Kb and 4Mb. I/O on these boundaries will be split across disks. You SAN administrator should be able to tell you the SAN allocation size. It the allocation size is small it might be an advantage to align your partitions and block sizes with that of the SAN.

I generally look at sar output to see if Disk I/O is getting to be a problem. You will see average queue size and service times increasing when you have an I/O problem. At that point you need to start looking at why I/O is a problem. With a SAN it could occur at a number of places. There are a variety of solutions. For virtual machines, I would lean separate SAN disks for each machine. These can be allocated as raw disks to the virtual machines rather than one of the virtual disk in a file formats like VMDK.

Disk alignment used to be rather trivial to figure out. All the tracks had the same number of sectors of the same size. Modern high density drives use variable numbers of sectors per track maintaining roughly the same bit density on the platter. They still report the old sizing information of cylinders, tracks, and sectors. Actual sector geometry varies depending on where on the disk it is being written.

Actual addressing is usually done in LBA (Logical Block Addressing) format. And really doesn't care about the disk geometry. Split I/Os are likely to be done by the disks control software. You may get split I/Os where you don't expect them, and not where you expect them.

Put those disks in a SAN and share them out, and the geometry gets hidden behind another layer of geometry. At that point I wouldn't even try to hazard a guess at which I/Os were split when. I would be more interested in the SANs view which will likely stripe the data in some size which is a power of 2, likely somewhere between 4Kb and 4Mb. I/O on these boundaries will be split across disks. You SAN administrator should be able to tell you the SAN allocation size. It the allocation size is small it might be an advantage to align your partitions and block sizes with that of the SAN.

I generally look at sar output to see if Disk I/O is getting to be a problem. You will see average queue size and service times increasing when you have an I/O problem. At that point you need to start looking at why I/O is a problem. With a SAN it could occur at a number of places. There are a variety of solutions. For virtual machines, I would lean to separate SAN disks for each machine. These can be allocated as raw disks to the virtual machines rather than one of the virtual disk in a file formats like VMDK.