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by Herbert_Sherbert
09/07/15 10:34 AM
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#17009 - 10/15/02 11:37 PM Re: Swap partition not being used
Energy Offline
Junior Member

Registered: 10/04/02
Posts: 21
Three points on swap:

First, when RAM was very expensive they use to recommend 2 1/2 times the amount of RAM. (i.e. on a 1 gig drive with 32 Megs of RAM 80 Megs was an acceptable amount of disk waste.) Now remember that this figure came about because either the machine was in a multi-user environment or was a workstation trying to run graphic intensive programs (i.e. Pro-E, AutoCAD, etc.) For those who have never had the fortune to be in this kind of environment we are only talking pre-1995 here.

Second, most systems today do not need this much swap space. However, when you get into serious server environments swap can begin become critical. For instance large SGI servers, if they crash and core dump (write their RAM to disk), need as much swap as memory. The core dump file can then be analyzed for why the system crashed. Also, large databases often use extensive swap.

Third, if you get into a situation where you really need to worry about swap there are some tuning tips. The simple ones are use multiple smaller swap partitions and spread them across disks.If running a database avoid putting swap on the same disks as the database or transaction logs.

One of the advantages to commercial operating systems is how they handle I/O (input/output.) Linux and the BSD's have come a long way but fiber channels, neural design, swap, multi-processors are still the areas the big boys excel in.

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#17010 - 10/16/02 01:50 AM Re: Swap partition not being used
Le4rner Offline
UGN Supporter

Registered: 03/05/02
Posts: 562
God I am such a n00b in here.

What are fiber channels and neural design,?

#17011 - 10/16/02 02:58 AM Re: Swap partition not being used
Energy Offline
Junior Member

Registered: 10/04/02
Posts: 21
That is actually a great question. I apologize for not answering it in my last response.

As bus speeds and processors become faster through Moores law the old hard drive wiring became the bottleneck. 160 MB Ultra SCSI-3 was not fast enough. Also, as you increased the number of disks being used to increase server capacity into multi-terabytes the distance between the hard drives and the bus became to large for SCSI technology. They therefore went to fibre channels to increase bandwidth and distance. (Notice I fixed my spelling. It is fibre according to SGI.)

As a side note, when you look at the speed of IDE drives today (ATA 100, 133, and 150) people often assume that these speeds make SCSI obsolete. This is actually not the case. The advantage to SCSI is that much of the machine's I/O load is offloaded to the SCSI processor. This frees the CPU to perform other activities. You will notice this when you transfer a large file (a few hundred MegaBytes) across a hard drive. The OS becomes very sluggish because the CPU is having to manage every byte being transfered. (To notice this on Unix machines you have to move the file across partitions, since Unix is smart enough to just move the inode assignment.)

Now for neural design. In very large servers you purchase processors in groups, usually four, and not in single units. This is because those processors are designed to work much as your brain does, calculating how to balance the load between both them and the other CPU clusters. (Sorry clusters is a term I made-up. SGI calls them bricks.)

If you look at
(click on the top link) and glance through the 3800 specs you will get a quick overview of large server class technology. I choose SGI because they own Cray.

calls their fibre channel a Fireplane, boasting a 172.8 GBps peak bandwidth, and also sell their processors in groups of 4.

Now I don't want you to think I have slighted the free OS's by what I have said. It is just a matter of economics. When a machine costs millions of dollars you just don't have time to port Linux to the machine. Capitalistic principles say it needs to be in production quickly. SGI, Sun, etc. have no reason to spend their time porting Linux. Since 8 and 16 processor machines have dropped in price Linux has been ported to them.

#17012 - 10/16/02 03:21 AM Re: Swap partition not being used
hKzKnight Offline

Registered: 03/12/02
Posts: 626
Loc: LAN
Just side note I think IBM also has their version... Never know, I've seen all sorts of fun things from IBM. All should go to the World Linux expo, I'll be there this yr. Anyway, sorry get side tracked.
"The ghost... Was never there and you'll never see me"

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