Re: 2 questions re RAID

On 06/17/2011 01:02 PM, Scott Ribe wrote:
> 1) Is my impression correct that given a choice between Areca& Highpoint, it's a no-brainer to go with Areca?
>

I guess you could call Highpoint a RAID manufacturer, but I wouldn't do
so. They've released so many terrible problems over the years that it's
hard to take the fact that they may have something reasonable you can
buy now (the 43XX cards I think?) seriously.

> And, in further digging, I discover that gh is an option for me. Anyone got comments on these? (I notice that they use ultracapacitor/flash to protect cache...)

Atto is so Mac focused that you're not going to find much experience
here, for the same reason you didn't get any response to your original
question. Their cards are using the same Intel IO Processor (IOP)
hardware as some known capable cards. For example, the ExpressSAS R348
is named that because it has an Intel 348 IOP. That's the same basic
processor as on the medium sized Areca boards:
http://www.areca.us/products/pcietosas1680series.htm So speed should be
reasonable, presuming they didn't make any major errors in board design
or firmware.

The real thing you need to investigate is whether the write cache setup
is done right, and whether monitoring is available in a way you can talk
to. What you want is for the card to run in write-back mode normally,
degrading to write-through when the battery stops working well. If you
don't see that sort of thing clearly documented as available, you really
don't want to consider their cards.

> 2) I understand why RAID 5 is not generally recommended for good db performance. But if the database is not huge (10-20GB), and the server has enough RAM to keep most all of the db cached, and the RAID uses (battery-backed) write-back cache, is it sill really an issue?
>

You're basically asking "if I don't write to the database, does the fact
that write performance on RAID5 is slow matter?" When asked that way,
sure, it's fine. If after applying the write cache to help, your write
throughput requirements don't ever exceed what a single disk can
provide, than maybe RAID5 will be fine for you. Make sure you keep
shared_buffers low though, because you're not going to be able to absorb
a heavy checkpoint sync on RAID5.

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