When you SHOULD move the Windows Pagefile
(and when you should not)
If you have only ONE PHYSICAL DISK DRIVE, do NOT move it. Leave it
where the default build put it, in the root of the c: drive (you won’t
see it there, unless you can view system and hidden files)
If you have MORE THAN 1 PHYSICAL disk drives, NOT just “drive
letters,” (partitions) on one disk drive, you should move it.
The reason for moving it is very simple – the reason for NOT moving
it is not obvious, but it makes sense, when you understand it.
- The rule is simple, but a little hard to say, if you try to say
it fast. You SHOULD move the swap file to the MOST BUSY PARTITION
on the LEAST BUSY disk drive.
If you have only one disk drive, then the rule means that you should
LEAVE IT on the windows “Boot” drive (which will, almost always be the MOST
BUSY PARTITION on the disk drive. Unfortunately, we have, by common usage,
come to equate a “partition” to a “drive letter” to a “drive!” NO! A
partition or drive letter is NOT a disk drive. If you don’t know the
difference, the best decision is to leave it on the C: drive where the
install program put it.
If you have more than one PHYSICAL disk drive, and you intend to use it for
your pagefile, you will need to know which “drive letter” represents the
root of each additional drive. (It is not always D:). If that additional
drive is “partitioned” then you will have to decide which is the “MOST BUSY
PARTITION,” then set the swap file to that drive letter. Windows Disk
Manager can be used to see the mapping between physical drives and drive
letters.
Unfortunately, Windows maps the pagefile to a "drive letter,"
with no clue as to which physical disk that drive letter exists on .
In fact, as you add disk drives and/or partitions, Windows actually
changes the drive letter that could map to the same physical sector.
If you have a second (or third) PHYSICAL disk drive, you can unload
the disk accesses for swap file, and keep all disk accesses on the
Windows Boot partition to run the Windows system, by moving the pagefile
to another physical spindle. be careful to follow the rule - don't
just put the pagefile on the first drive letter on that physical disk.
Be sure the swap file is on THE MOST BUSY PARTITION (or drive letter).
For instance, if you have a 2nd physical disk, with two partitions - one
has a very busy database file on it - the other is only used to store
system state backups. The obvious location for the very busy
pagefile is NOT OBVIOUS - you should put it on the same partition that
the database file is on.
Too often, the certification tests (written by “experts” who do not
understand hard disk dynamics) will state, unequivocally, that you
should move the swap file to the D: drive, to improve performance. Nope!
If you have only ONE PHYSICAL DRIVE, that is partitioned into C: and
D:, they are both on the same physical drive. You have not put
the swap files on different drives just different drive letters
(PARTITIONS). You may think there are two drives but the platters and
heads do the reading and writing on the SAME DRIVE.
For a disk drive head to access a FILE (swapfile) on the current
partition, it's simply a matter of moving the head to the appropriate
track and waiting for the file's sector to rotate under the head.
Total time is one seek and one rotational latency.
IF the disk drive head has to access the page file on another
PARTITION OF THE SAME DISK, the disk must move the head to the
synchronization track, read the disk architecture, move the head to to
track that contains the directory for that new partition, wait for
rotational latency, THEN read the location of the root files for that
partition (where the swapfile will be located).
THEN the head has to do the same thing as it would have, to access
the pagefile on the SAME PARTITION.
This total process of changing PARTITIONS on the same physical disk
drive takes EONS more time and disk cycling than simply moving to the
swap file on the (most busy) BOOT PARTITION (where the head is most
likely to be at any given instant of time).
By choosing the MOST BUSY PARTITION on the LEAST BUSY DISK DRIVE, you
gain the benefit of NOT having to locate, seek, and MOVE TO ANOTHER
PARTITION on the swap drive.
If you put the swap files on different PHYSICAL DISK DRIVES so that
the applications do not try to access their data at the same time and
therefore have to wait on each other, they are not fighting for access
to the heads/platter position. Both the system accesses and the
swap file accesses can be accomplished in ONE SEEK and ONE ROTATIONAL
LATENCY, virtually simultaneously.
One thing you need to keep in mind is that the drives need to be on
separate controllers as well, if you really want to really optimize
swapfile access. If not then they are going to be sharing the same
controller and end up with a bottleneck there, but this is not a serious
bottleneck.
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06/28/2009
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