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Old 09-03-2004, 12:25 AM   #1
Thaidog
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Question Trying to spped things up with multiple scsi disks...


I have a couple of scsi disks that I would like to install my system on...

Is there certain filesystems that access each other at the same time? (during boot or applications launching etc)

I'm wondering how to partition my new system... like if it would speed things up if I put say the /usr filesystem on one disk and the swap on another if it would speed things up...?
 
Old 09-03-2004, 01:27 AM   #2
Dark_Helmet
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That kind of speed up doesn't involve the filesystem. What would help is how you physically connect the drives.

When you connect a disk drive to a controller, only one device can talk to the controller at one time. This is because of the cable connecting them. The wires simply cannot transmit multiple "conversations" at once. So, it never actually gets to the filesystem level; the bottleneck is in the physical connection.

This is why you will see people put their heaviest use drives on separate controllers. Say you want faster virtual memory access. You would put the drive with your swap partition on one controller, and the drive with your data partition on a different controller. As an example, say your memory is full (i.e. you're using swap space), and you launch a new application. The computer can tell the disk with the program to start reading the data, and at the same time, tell the disk with the swap partition to start "paging out" data in memory to make room for the application you just started. Both drives are working in parallel now rather than one at a time if they were connected to the same controller.

Now, your choice of filesystem might have in impact on how long it takes for the drive to read or write data, but the filesystems themselves can't offer multiple, simultaneous access.

For SCSI, you can probably see a problem. Depending on your controller, you can have 15 devices plugged into it. That means they are all competing for the controller's attention. Again, only one conversation can occur over the wire at once. SCSI tends to be faster than IDE for various reasons (mainly raw data transfer speed), but the gap is closing between IDE and SCSI. To my knowledge, SCSI tends to be more efficient in handling traffic, but I'm not that knowledgeable about IDE protocol.

So, what I'm trying to say is this: using SCSI drives won't necessarily speed up your machine. If they do, it would be a comparison similar to upgrading the speed of your processor. Using separate controllers would be comparable to getting a second identical processor instead of a single faster one. Unless SCSI gains you twice the transfer speed of IDE, then it may be more efficient to just move your IDE devices around.

It's not quite that simple, but it's good enough for government work
 
Old 09-03-2004, 01:49 AM   #3
Thaidog
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I actually have multiple controllers... what I'm really trying to find out is what filesystems access each other simultaneously in certain situations... like at boot time or when opening an application...

Example... when opening application "A" the OS sends requests to both the var and the usr filesystem at the same time (or close to the same time...

To speed up access I put var and opt on seperate disks and separate controllers.

So what I'm looking for a partitioning combo for my workstation that optimises the filiesytem by putting the filesystem partitions on multiple drives and controllers.

Last edited by Thaidog; 09-03-2004 at 02:04 AM.
 
Old 09-03-2004, 02:32 AM   #4
Dark_Helmet
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My mistake, I thought you meant filesystem as in ReiserFS, ext3, ext2, etc.

I can't offer a specific solution, but I would imagine a minimum of three controllers.

A dedicated swap partition. Again, if you have a lot of services or users, things will be moving in and out of memory quite a bit. So I would imagine this would be a strong candidate for a separate controller.

You binaries, service daemons, libs (any executables or runtime support files) could benefit. It goes hand-in-hand with the swap partition. You'd want to swap out to disk when launching a new program. So your binaries and swap should definitely be on separate controllers.

Assuming your logs are all programmed to go into /var somewhere, it might be worth it to put /var on a separate controller. If your system handles a lot of services and/or users, the you ought to have a semi-constant stream of writes to that location (not to mention if you have mail and print queues there as well).

Maybe the /home directories after that, or project directories if you're administering that type of machine.

I wouldn't worry about putting anything like /etc, source code, or doumentation (like man pages). Those are obviously not used frequently, or are not performance-critical.

Of course, it all depends on what's running in your system and how it's used. If I had the hardware, that's roughly the order I would set them up in. Your mileage may vary...
 
Old 09-03-2004, 02:43 AM   #5
DavidPhillips
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High end SCSI and IDE drives are practically the same on a single drive system. The problem with IDE is the bandwidth available. Under heavy load the IDE just will not provide the necessary bandwidth for a server. The SCSI system can access more devices much better than is possible for IDE systems. This is mainly why SCSI will be used on servers under a heavy load. Also the SCSI drive is more durable, standing up to a lot more heat without damage.

SCSI drives are well suited for RAID arrays which would speed up your read capabilities without slowing down the write time. Basically you can almost double your read speed by creating a RAID mirror array out of the drives. This is a far greater improvement than you will see by arranging partitions. If you were to loose a drive from the mirrored array the system will continue to operate.

On a normal desktop system the read speed is more important than the write speed. Once apps are installed they are read from the drive into memory. Then the data is discarded. Not much is actually written back to the drive under most conditions. You do want to avoid using swap space if it's at all possible, as this constitutes constantly writing back to the drive.

Last edited by DavidPhillips; 09-03-2004 at 02:46 AM.
 
Old 09-03-2004, 03:49 AM   #6
r0b0
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1. Put a small swap partition on each drive instead of dedicating one drive for big swap.
2. Consider using RAID, either hardware-based (if your controller cupports it) or software (raidtools or modern LVM).
3. If you're not going with a RAID solution, just put /usr, /var, /home on different disks.
4. Filesystem - I recommend reiserfs.
 
Old 09-03-2004, 05:43 AM   #7
Thaidog
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Quote:
Originally posted by r0b0
1. Put a small swap partition on each drive instead of dedicating one drive for big swap.
2. Consider using RAID, either hardware-based (if your controller cupports it) or software (raidtools or modern LVM).
3. If you're not going with a RAID solution, just put /usr, /var, /home on different disks.
4. Filesystem - I recommend reiserfs.
I'll be using XFS... I've got some pretty big files I'll be moving around... that's why XFS. It's supposed to be around the same speed as reiserfs.

When you say put swap on more than one disk do you mean raid? ...or can you actually have more than one /swap that the system understands correctly?
 
  


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