Partition Designators

Does the hd(x,x) format for specifying partitions/drives skip numbers for an extended partition? I know that sda, sdb, etc. method skips partition numbers, e.g. on my SATA drive with one extended partition, it skips three numbers:

/dev/sda
/dev/sda1 NTFS
/dev/sda2 Extended <= (start of extended partition)
/dev/sda5 Linux native
/dev/sda6 Linux native
/dev/sda7 Linux swap
...etc...

So I think this would be hd(0,1) for sda1, but I don't know if hd(0,5) is correct for sda5.

Also, is it preferable to put the swap file on a separate drive (on another SATA channel)?

Thanks!
Patti

Hi
Name of the game is to subtract 1. sda, sdb, sdc --> hd0, hd1, hd2
sda1, sda2, sda3 --> hd0,0 hd0,1 hd0,2
sda5, sda6, sda7 --> hd0,4 hd0,5 hd0,6

Primary partitions go 1,2,3 up to 4
sda1 is (hd0,0)

Logical partitions in the extended partition always start at 5 and run as 5, 6, 7....
sda5 is (hd0,4)
Swerdna

Hi
Name of the game is to subtract 1. sda, sdb, sdc --> hd0, hd1, hd2
sda1, sda2, sda3 --> hd0,0 hd0,1 hd0,2
sda5, sda6, sda7 --> hd0,4 hd0,5 hd0,6
Primary partitions go 1,2,3 up to 4
sda1 is (hd0,0)
Logical partitions in the extended partition always start at 5 and run as 5, 6, 7....
sda5 is (hd0,4)
Swerdna
[/b]

There's the little catch! I didn't know that extended partitions start at 5. (I don't think a second extended partition is allowed.) The numbering just starts at zero for hd(x,x). THANK YOU!!!!!!!!!!

:blink: Patti

Also, is it preferable to put the swap file on a separate drive (on another SATA channel)?
[/b]

It may increase performance when your swap is on a device/channel that is not very much used for other reasons. For he same reasons that it helps to put any chunks of data very heavily used on different disks/channels.

When you use a database heavily and swap heavily at the same time on the same disk your read/write heads will move a lot. You will understand that this may slow down your system.
A solution in such a case may also be put the database on a different disk. The swap is then on what we may call the "system disk" and swap I/O is then shared with things like program loading, which (on a database sever) may not be very heavy usage.

Same: on a heavily used http server put your webpages on a different channel/disk.

So measurements to increase performance depend very much on the intended usage of the system (this results in many "maybe"s :lol: ).

It may increase performance when your swap is on a device/channel that is not very much used for other reasons. For he same reasons that it helps to put any chunks of data very heavily used on different disks/channels.

When you use a database heavily and swap heavily at the same time on the same disk your read/write heads will move a lot. You will understand that this may slow down your system.
A solution in such a case may also be put the database on a different disk. The swap is then on what we may call the "system disk" and swap I/O is then shared with things like program loading, which (on a database sever) may not be very heavy usage.

Same: on a heavily used http server put your webpages on a different channel/disk.

So measurements to increase performance depend very much on the intended usage of the system (this results in many "maybe"s :lol: ).
[/b]

If you run in trouble with performance it is possible to have two swap partitions on two different drives (mounted with the same swap priority) which causes a distributed swap usage (like raid 0). But I think normally this is not necessary any more

usually 1 swap per disk (number of swap partitions on 32-bit intel is limited)
set properly swappiness for efficient desktop/laptop swap usage
you can always add swap file if more swap is needed.

constant swapping in the case of db should be avoided (get more RAM). setting properly memory for db usage is not as trivial as setting swap.

irrelevant of the RAM amount you should always have swap activated

usually 1 swap per disk (number of swap partitions on 32-bit intel is limited)
set properly swappiness for efficient desktop/laptop swap usage
you can always add swap file if more swap is needed.

constant swapping in the case of db should be avoided (get more RAM). setting properly memory for db usage is not as trivial as setting swap.

irrelevant of the RAM amount you should always have swap activated
[/b]

regarding swap, i always believed you were meant to have roughly swap in GB as what you have ram in GB. so i have 2GB swap as i have 2GB ram. yet when always checking with ctrl+esc, swap is nearly always using 0KB. even when i'm using a lot of processed etc. why is this broch? (or anyone else, of course)

as said several times, on the forum, *nix's will use real ram before using swap,and it needs to be something REALLY memory intensive for swap to even be thought of used

Andy

@thestig
depends on RAM amount.
depends on applications (with 16GB of RAM, advised swap is 8GB anyway, so half of RAM).
efficient memory usage will also depends of shmmax settings, also shmall settings are adjustable (for a standard desktop, default settings are o.k.)
and so on

I would say that 1.5x of RAM up to 4GB of RAM is safe. Considering disk sizes this is not that much.
If you have 2GB of RAM and 2GB of swap then you are just fine if you don't see swap activity.


The only really, really wrong memory policy is disabling swap (for "speed"). Irrelevant of the amount of RAM installed. Andrew Morton talked about this sometime ago. I will not repeat how he called users who disable swap. It boils down to the lack of understanding of memory management.
Simply keep swap file/swap partition on your box.