Need Guidance re: Striped Swap Partitions

bpont · 2012-01-11 21:48:16

I have two swap partitions on two separate hard drives of differing manufacturers, ages and speed. Using the most current source of information I could find (2003), it says that swap spaces
with equal priorities will be striped. My question is whether this is actually a wise strategy considering the differing speeds of my two hard drives. I thought I'd seek some advice regarding possible problems or issues before making such fundamental changes to my system.

brando56894 · 2012-01-12 00:29:24

How much RAM do you have? Swap isn't necessary with about 4GB+ of RAM.

bpont · 2012-01-12 05:00:20

brando56894 wrote:

How much RAM do you have? Swap isn't necessary with about 4GB+ of RAM.

I have 1GB of RAM

Jristz · 2012-01-12 06:20:18

In may experienmce
Swap in same hdd that / (root) or /tmp or /var = only i you have 1 HDD
Swap in seccond HDD diferent from avove directoryes good idea

other thing is set te swappiness (or someting like this) to about 20-10 for maximize RAM usage

bpont · 2012-01-12 19:05:40

Jristz wrote:

In may experienmce
Swap in same hdd that / (root) or /tmp or /var = only i you have 1 HDD
Swap in seccond HDD diferent from avove directoryes good idea
other thing is set te swappiness (or someting like this) to about 20-10 for maximize RAM usage

Good advice, but what I really needed was an answer to my specific question.

Awebb · 2012-01-12 19:35:48

Interesting thought. You expect problems, because the read/write speed of the two disks is different, that's why you are worried, that something time critical could break, because probably two chunks of the same file might be loaded from both disks at the same time. I have no experience with this exact scenario, but swap is expected to be slow and unreliable to begin with. If swapped data has to be read, the kernel can expect other, random, reads and writes to the disk until it can access the swap space (and if it's just logfiles being written to the disk or you downloading cat pictures via torrent). Swapping generally is not that time critical. I'd say, as a rule of thumb, if you can live without a real time kernel, you don't have to worry about any probable syncing problems between two swap disks. You might run into such problems, if you have two swap partitions on the same disk, then your HDD head had to travel back and forth, in order to distribute and fetch the swapped data.

It should behave analogue to LVM/Raid0, they don't make notable trouble when dealing with differently performing disks. I don't know of any problems with your setup.

Last edited by Awebb (2012-01-12 19:38:20)

bpont · 2012-01-12 22:10:51

Awebb wrote:

Interesting thought. You expect problems, because the read/write speed of the two disks is different, that's why you are worried, that something time critical could break, because probably two chunks of the same file might be loaded from both disks at the same time. I have no experience with this exact scenario, but swap is expected to be slow and unreliable to begin with. If swapped data has to be read, the kernel can expect other, random, reads and writes to the disk until it can access the swap space (and if it's just logfiles being written to the disk or you downloading cat pictures via torrent). Swapping generally is not that time critical. I'd say, as a rule of thumb, if you can live without a real time kernel, you don't have to worry about any probable syncing problems between two swap disks. You might run into such problems, if you have two swap partitions on the same disk, then your HDD head had to travel back and forth, in order to distribute and fetch the swapped data.
It should behave analogue to LVM/Raid0, they don't make notable trouble when dealing with differently performing disks. I don't know of any problems with your setup.

So if I'm interpreting your comments correctly, I really don't have much to worry about since each partition is on a separate hd.

Awebb · 2012-01-12 22:53:58

Yes. This guy here (http://kerneltrap.org/node/5247) even claims, that I'm wrong and multiple swap spaces on a single disk can speed things up.

bpont · 2012-01-12 23:30:28

Awebb wrote:

Yes. This guy here (http://kerneltrap.org/node/5247) even claims, that I'm wrong and multiple swap spaces on a single disk can speed things up.

Great...I'll test things out and see if there's a noticeable performance boost. Thanks again for your help.

Arch Linux

#1 2012-01-11 21:48:16

Need Guidance re: Striped Swap Partitions

#2 2012-01-12 00:29:24

Re: Need Guidance re: Striped Swap Partitions

#3 2012-01-12 05:00:20

Re: Need Guidance re: Striped Swap Partitions

#4 2012-01-12 06:20:18

Re: Need Guidance re: Striped Swap Partitions

#5 2012-01-12 19:05:40

Re: Need Guidance re: Striped Swap Partitions

#6 2012-01-12 19:35:48

Re: Need Guidance re: Striped Swap Partitions

#7 2012-01-12 22:10:51

Re: Need Guidance re: Striped Swap Partitions

#8 2012-01-12 22:53:58

Re: Need Guidance re: Striped Swap Partitions

#9 2012-01-12 23:30:28

Re: Need Guidance re: Striped Swap Partitions

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