RAID Card Memory -- Should I upgrade it?

GCS

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Oct 16, 1999
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I managed to get an Areca ARC-1170 for a good price and it comes with it's stock ram (256mb). It is upgradeable to 1GB.

Is it worth it to move up to the 1GB?

I will using for a Home Media Server in a Norco 4020 Case. I'll start with 6 1TB WD Green Drives and eventually move to 20 as I need to.

If I should move up the ram do I have to get their specific module or does anyone know if I can get a generic SODIMM to work safely on the card?

Greg
 

Blain

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Oct 9, 1999
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Originally posted by: GCS
Areca ARC-1170 RAID Card --- worth it?

I just scored one for $350 (card only no cables)...
You didn't get the battery backup card also?

 

Fullmetal Chocobo

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Originally posted by: GCS
Nope

Then that is also your answer. The more cache you have on the card, the more data you will lose if you lose power to that machine. That data sits in cache while waiting to be written to the hard drive. Power dies = data dies. With the battery backup, it will store that data.... I'd leave that cache where it is currently unless you plan to put a battery module on that card (which isn't a bad investment, if you plan to work the arrays on the card).
 

GCS

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Well the server will be streaming videos to multiple Media Extenders throughout the house and will most likely be running 24/7. It will be on a 1500VA UPS System as well.

Greg
 

RebateMonger

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BBU is important if Write-Back Cache is enabled. Even more so with RAID 5, which is pretty vulnerable to corruption. But considering that you are likely mostly streaming videos, plus you have a strong UPS, it's not likely to make much difference one way or another.

Considering that a ten-year-old PC can likely stream videos just fine, you probably don't really need a 1 GB cache. Unless you are seeing a stuttering problem, I wouldn't bother.
 

GCS

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Sounds like a plan.

I will actually be running (2) RAID 6 arrays in this server (10 drives per array) and yes all it will be doing is storing and streaming videos, pics, and music to Media Extenders.

The system will be more powerful than necessary (Supermicro Server motherboard, 4gb of DDR3 ram, e8400 CPU, and an Sapphire HD4350 HDMI video card). I will probably get the BBU for it anyway just to be safe.


Thanks for the info guys!

Greg
 

pjkenned

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Well, you are talking what 2 GigE ports being served by 20 drives doing sequential reads?
So you have 20x drives in two raid 6 arrays? Each drive is capable of 120MB/s. So that's 2.4GB/s theoretical bandwidth from the drives
IOP331 on that ARC-1170 is 800MHz is probably good for raid 6 800MB/s.
PCI-X is around 1.06GB/s

But...

200ish MB/s bandwidth out of the server with dual GigE ports and cache isn't going to be a limiting factor. If you were using the array locally, more cache and a IOP348 wouldn't be a bad upgrade. For streaming 256MB isn't going to be bad with a low number of clients.

Also, with no BBU on that array, disabling the cache isn't a bad idea necessarily. You are trusting your data to a 10-15 minute battery rather than a 3 day battery, that can be moved machine to machine.
 

Rubycon

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Aug 10, 2005
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UPS is NOT a substitute for a transportable BBU no more than RAID is a substitute for real backups.

Why? plenty of reasons. Accidents happen. The UPS is useless if the power cord is unplugged. A fault causing the sudden power off of the system, a BSOD where a hard reset (full power off) is required - the BBU will hold the cache contents. Even in such an event the OS itself can become corrupt combining that along with up to 1+ gigabyte of uncommitted data LOST can really make recovery a PITA!

Bottom line - if you want to get the most performance from your cache by using write back with delay - a BBU is a MUST.
 

Idontcare

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Originally posted by: Rubycon
Bottom line - if you want to get the most performance from your cache by using write back with delay - a BBU is a MUST.

If you find yourself in a situation where you lose your data because you did not have a BBU then you were going to lose your data regardless how your cache is configured, even if the cache is disabled.

BBU is kicked in because system went down, if cache is disabled (or operating in a slow mode) then your data was in the system's ram went down instead of the cache and was lost when the system crashed.

To my knowledge there is nothing about the BBU that enables a safer higher performance environment, it makes an existing higher performance environment safer but there is no such thing as operating without a BBU and configuring any aspect of your arrays or your cache mode so as to operate with same safety but reduced performance.

There's safety and then there's performance and to my knowledge when it comes to BBU these are orthogonal and have nothing to do with each other any more than a PSU determines how much performance your ram can deliver.
 

Rubycon

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I've tested this both ways and found with the cache light ON (data in buffer) if the battery wire was lifted and then placed back in the system there would ALWAYS be corruption vs. doing nothing leads to a usable system. So in that case it does indeed work. :)

I've also been told but this is officially unconfirmed that the Areca cards tend to delay their flushes more aggressively when a battery is present. I have no real way to positively validate this but if true it's a good thing. I miss the flush settings in the original megaraids.
 

specialk90

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Apr 14, 2009
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I have a 3ware 8port Sata PCI-E controller and a very powerful UPS but no BBU.

I just checked my Alarm status on my 3ware card and found exactly why you should use a BBU. Here is what it said from a Bad Sector:
"The 3ware RAID controller supports a feature called dynamic sector repair that allows the unit to recover from certain drive errors that would normally result in a degraded unit situation. For redundant units such as RAID 1, 5, 6, 10, and 50, the 3ware RAID controller essentially has two copies of your data available. If a read command to a sector on a disk drive results in an error, it reverts to the redundant copy in order to satisfy the host?s request. At this point, the 3ware RAID controller has a good copy of the requested data in its cache memory. It will then use this data to force the failing drive to reallocate the bad sector, which essentially repairs the sector."

I hope your card can do this. Also, a bad sector read can cause other problems if this nice feature was not available.
 

GCS

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Oct 16, 1999
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Well does anyone know if a generic DDR SODIMM will work in an Areca card or do I have to go with their $100 1GB SODIMM?

BBU has been ordered.

Greg


EDIT - Screw it. I ordered the ram and BBU. Better to be safe than sorry.

 

Idontcare

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Oct 10, 1999
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Note: before anyone gets the idea that I am waging some manner of forum war against BBU's please realize I have nothing against BBU's and the value they add. What I am attempting to do is bring clarity to what tends to be an over-attributed value proposition with BBU's. BBU's add value, but folks tend to go a little overboard with how, where, and why they add value. When misinformation gets created and then debunked at a later stage it tends to undermine the otherwise credible value-add aspects of BBU's and this in turn does result in posters coming out in full force as anti-BBU (the "its a waste of money" comments). All I am attempting to do here is make sure that comments regarding the value a BBU brings to the user is not overstated.

Originally posted by: Rubycon
I've tested this both ways and found with the cache light ON (data in buffer) if the battery wire was lifted and then placed back in the system there would ALWAYS be corruption vs. doing nothing leads to a usable system. So in that case it does indeed work. :)

I've also been told but this is officially unconfirmed that the Areca cards tend to delay their flushes more aggressively when a battery is present. I have no real way to positively validate this but if true it's a good thing. I miss the flush settings in the original megaraids.

I'm not saying the BBU doesn't add value in terms of increasing the chances that your data are not lost, there is no question here.

But BBU's are not about performance, there is no situation we can construct for which a computer would not lose data without the BBU (regardless of performance) but with a BBU it would not only not lose the data but would also operate at higher performance too. I'm pretty sure I am saying that correctly, but it might not read too easily.

Originally posted by: specialk90
I have a 3ware 8port Sata PCI-E controller and a very powerful UPS but no BBU.

I just checked my Alarm status on my 3ware card and found exactly why you should use a BBU. Here is what it said from a Bad Sector:
"The 3ware RAID controller supports a feature called dynamic sector repair that allows the unit to recover from certain drive errors that would normally result in a degraded unit situation. For redundant units such as RAID 1, 5, 6, 10, and 50, the 3ware RAID controller essentially has two copies of your data available. If a read command to a sector on a disk drive results in an error, it reverts to the redundant copy in order to satisfy the host?s request. At this point, the 3ware RAID controller has a good copy of the requested data in its cache memory. It will then use this data to force the failing drive to reallocate the bad sector, which essentially repairs the sector."

I hope your card can do this. Also, a bad sector read can cause other problems if this nice feature was not available.

No argument that this is a nice feature but I don't see where it is a feature strictly enabled by the presence of a BBU. How is it that this feature requires a BBU in order to function?
 

Rubycon

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Aug 10, 2005
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I'm not advocating performance increases with a BBU at all. It's not recommended to use write back cache at all when a BBU is absent. Many controllers will not allow the cache to be set when this condition exists. This results in lower performance and in the case where it's locked out you will have higher performance with a BBU.

You CAN use most ECC UNBUFFERED DIMM on these cards. The 2GB module is about $30 U.S. from Crucial and works perfectly.
 

pjkenned

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Originally posted by: GCS
Well does anyone know if a generic DDR SODIMM will work in an Areca card or do I have to go with their $100 1GB SODIMM?

I just hope that's a "generic ECC DDR..." as you really do want ECC memory for a raid controller's cache even with the extra latency.

And this BBU vs UPS debate is easy to figure out... use both on any critical system when applicable. A few bucks spent on these batteries is recovered in one hour of recovery labor/ my time. Also, most decent UPS's also have a certain amount of surge protection, high/low voltage protection, and system shut-off as features meaning it is a good idea to spend $110-$130 on a raid card BBU, but to spend well north of that on a decent UPS.
 

GCS

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I went with the Areca "branded" Ram and BBU from Newegg.

Cost me a little more than I probably could have gotten them for elsewhere (or going generic) but at least this way I should have exactly what works with the card.

Greg