Cisco 2821 - Above memory requirements. What happens?

[juandcc2014]

Hello.

I currently just got a Cisco 2821 with CallManager(8.6) installed and IOS(15.1M) and ADVENTERPRISE installed. It has 512MB of DRAM and 256MB of Compact Flash memory. This device will solely be used for VoIP.

I was wondering if it would be enough for managing about 12 IP Wired Phones(7940s), and 12 IP Wireless Phones(7920s) under full load, utilizing all of the CME features with no limitations. If not, I was thinking on upgrading both the CF and DRAM.

I have been looking at forums saying that 2Gb should be the max of CF. If so, what brands are recommended? Is it safe(any potential issues)?

As for the DRAM, I read that 1GB is the max. But people have been going over 512MB for the CF, so I'm wondering if one can go over 1GB for DRAM. And if so, what would be the maximum?

[Joseph W. Doherty · Accepted solution]

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@juandcc2014 wrote:

I have been looking at forums saying that 2Gb should be the max of CF. If so, what brands are recommended? Is it safe(any potential issues)?

As for the DRAM, I read that 1GB is the max. But people have been going over 512MB for the CF, so I'm wondering if one can go over 1GB for DRAM. And if so, what would be the maximum?

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Datasheet notes max RAM for a 2821 is gig, and as that's usually a hardware design limitation, it's very, very unlikely you can exceed it.

BTW, as Call Manager 8.6 is long ago EoL/EoS, unable to find any resource requirements for it.

[juandcc2014]

Thank you for your reply. So you said that the Max RAM is 1Gb. Got it

As for the CF, would 2Gb be too much or should I stick with 1Gb CF? 

[Joseph W. Doherty]

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@juandcc2014 wrote:

As for the CF, would 2Gb be too much or should I stick with 1Gb CF? 

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Depends on what you anticipate you wish to store on your CF.  Of course, usually, you want enough space to save your IOS you're going to boot into.

The only thing, that comes to my mind, that uses flash memory, unexpectedly, is crash logs.

Beyond that, it's nice to have sufficient flash to hold the currently running IOS and the another the one you want to "upgrade" to.

[Jens Albrecht · Accepted solution]

Hello @juandcc2014,

for your setup with just a few phones the current 512MB of DRAM and 256MB of Compact Flash memory should be more than enough. The official maximum supported CF size for these routers is 256MB anyway. For DRAM the official maximum is 1GB but this is only needed e.g. for very large routing tables, not to make phone calls.

HTH!

[juandcc2014]

Thank you for your reply. 

You said the "official maximum supported" size. What is the "unofficial maximum". As in, what is the maximum that people normally go to that is beyond the maximum that the cisco data sheets specify but that still works?

[Joseph W. Doherty]

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@Jens Albrecht wrote:

For DRAM the official maximum is 1GB but this is only needed e.g. for very large routing tables, not to make phone calls.

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For a total of just 24 phones, and router only effectively running Call Manager, one would think that half a gig to gig would be sufficient RAM, however when trying to find RAM recommendations for Call Manager, I believe I found recommendations for providing 2 GB of RAM for every 10K daily phone calls.  Besides 10 K phone calls a day, is, I suspect, unlikely to be generated by just 24 phones, I was surprised the recommendation didn't appear to be related to total number of phones or maximum expected concurrent active phone calls, but a daily usage consideration.(?)

I've often supported VoIP running across the network, but I've never been involved sizing the equipment, so I have no idea how bandwidth demanding call manager might be.  Heck, right now, on my Windows 10 PC, I'm only running a browser with 7 open tabs, and task manager, and the latter says I'm using 6.7 GB!  So, Jens, is you belief that a gig would be ample is based on direct experience?  Further, for 24 phones, the currently installed half gig is insufficient?

[juandcc2014]

Is it possible I could use 1Gb DRAM chips meant for the 2900 series routers into the 2821 routers(are they compatible)? How about a 2Gb compact flash card meant for the 2900 series routers(are they also compatible with the 2821)?

[Jens Albrecht]

Sorry, but this is not possible. The good old 2821 uses ECC DDR (PC2100, 184-pin), while the newer 2900 series uses ECC DDR2 (PC2-5300, 240-pin). I still see no point in going beyond 512MB RAM for such a small setup.

[juandcc2014]

Alright, so the 1Gb RAM is the limit for the 2821. But what about the compact flash card? I saw a listing on Ebay for a 2Gb compact flash card meant for the 2900 routers. Could it still be used for the 2821?

[Joseph W. Doherty]

Alright, so the 1Gb RAM is the limit for the 2821. But what about the compact flash card? I saw a listing on Ebay for a 2Gb compact flash card meant for the 2900 routers. Could it still be used for the 2821?

It would be hit or miss, and has its own considerations.  Take careful note of both Leo's and Jens' recent replies.

[Jens Albrecht · Accepted solution]

We had to use the official Cisco CF memory as the routers were under TAC support and those 256MB cards were always sufficient. I remember that those routers were somewhat picky regarding 3rd party CF cards when people used them for their home labs. Some brands worked, others not but I don't remember any details, simply too many years ago.

[Leo Laohoo · Accepted solution]

Cisco-branded CF can only go up to 1 Gb but our 2821 was deployed with 2 Gb CF (read between the lines).

Our 2951, Sup720, Sup2T were deployed with 2 Gb CF too.