Cache Hits - Should I worry?

[iolair]

Gentlemen,
I recently upgraded my Compaq 5500 Server's ram from 1GB to 2.25GB of Ram because I read on Novell's website that if the Long Term Cache Hits fell below 90%, add ram. The Compaq Setup routine recognized the 2.25GB of Ram, and when I booted Netware 5.1, (sp8), it recognized the ram as well. So, I thought great, all is well.

In Monitor, System Resources went from 76% to 82%, so I thought great, this is going well. Then I checked the Long Term Cache Hits stats. Here are my stats, after 21 days:
Short Term Cache Hits 100%
Short Term Dirty Cache Hits 100%
Long Term Cache Hits 86%
Long Term Dirty Cache Hits 99%
LRU Sitting Time 11:00:36.4
Alloc Block Count 53,048,897
Allocated from AVAIL 541,293
Allocated from LRU 52,507,604

The Original Buffers were 589,112, and the total buffers is at 484,635. Yesterday, after sitting all weekend, the LRU sitting time was up to 2:18:12:33 (over two days), but when people are here using the server, it goes down below 15 minutes, and Novell says that is bad. I changed the Maximum Concurrent Writes from 100 to 300, and that helped a little, briefly, but then my LRU times went back below 15 minutes.

As far as I can tell, nobody has complained of any performance problems. I haven't seen any problems at the server. So, should I be worried about the Long Term Cache Hits being below 90%? This server is used only for authentication and file services.

Iolair MacWalter

 

[marvhuffaker]

With that much ram I would expect the LRU to stay pretty high. 15 minutes is generally not acceptable.

I have seen cases where the Long term cache hits sat around 80% and there was nothing we could do about it. It sort of depends on what you're doing with the server. In this one case, it was a Btreive database with a ton of storage. It was impossible to keep it in cache so it had to flush the buffers quite often.

It's also possible that right after rebooting, the numbers will be low like that. Until stuff can get into the cache, it's going to have to read everything from disk. Might want to see where it's at in a week.

As far as performance, there are 3 things that I check first thing on any 5.1 server I touch. They are always at the default which is way too low for todays servers with gig's of RAM. The settings are:

Minimum Directory Cache Buffers
Maximum Directory Cache Buffers
Directory Cache Allocation Wait Time

If these are at the defaults, your server will be sluggish no matter how much RAM you have.. Can you get the stats on what you currently have and we'll see if we can get that baby tuned to perfection.

I also assume you're running traditional volumes, not NSS.

Marvin Huffaker, MCNE

http://www.redjuju.com

 

[iolair]

Thanks Marvin. I believe the 3 settings are at the defaults.
Minimum Directory Cache Buffers = 150
Maximum Directory Cache Buffers = 500
Directory Cache Allocation Wait Time = 2.2 sec.

Yes, I am using traditional volumes. I have two 72GB drives, which are being mirrored by Compaq's hardware array setup. Currently, the disks hold 12Gb of data for users. I do have a copy of Netware 6, would it help to upgrade?

Thanks again, Marvin. I always appreciate your help.

Iolair MacWalter

 

[marvhuffaker]

Ouch. Those settings are terrible. I'm guessing that your current Directory Cache buffers are at 500 (on the main Monitor screen). Upgrading to NW6 won't help your problems. It's just a matter of tuning. You could make some minor tweaks and get that server running sweet.

Try this:

Set Minimum Directory Cache Buffers = 2500
Set Maximum Directory Cache Buffers = 5000
Set Directory Cache Allocation Wait Time = 0.1 Sec

Make these changes in Monitor, they'll stick (You don't have to put them in autoexec.ncf unless you want to).

Wait a couple days, then look at the Directory Cache Buffers stat in Monitor and report back on what it shows. We may need to adjust more, or it might be just right. You really want your current buffers to be right around the Minimum settings. Then double the max. You can expect it to take a couple days of good user activity to settle in.

Once you get that tuned, there may be some other things to look at..

Marvin








Marvin Huffaker, MCNE

http://www.redjuju.com

 

[iolair]

Thanks, Marvin. I've made those changes, let's see what happens in the next few days. I really, really appreciate it.

Iolair MacWalter

 

[iolair]

Marvin,
Those changes seem to have fixed it. I am getting 98% on the Long Term Cache Hits now, and the LRU sitting time is over two and a half days. Thank you so much.

Iolair MacWalter

 

[Trevoke]

Where CAN we find a place online, FAQ or anything, to find good settings for our servers?

-Haben sie fosforos?
-No tiengo caballero, but I have un briquet.