Re: RAID card recommendation - Mailing list pgsql-performance

From Karl Denninger
Subject Re: RAID card recommendation
Date
Msg-id 4B1D5BD5.1010806@denninger.net
Whole thread Raw
In response to Re: RAID card recommendation  (Scott Carey <scott@richrelevance.com>)
List pgsql-performance
Scott Carey wrote:
On 12/1/09 6:49 PM, "Greg Smith" <greg@2ndquadrant.com> wrote:
 
Scott Carey wrote:   
3ware 95xx and 96xx had performance somewhere between PERC 5 (horrid) and
PERC 6 (mediocre) when I tested them with large SATA drives with RAID 10.
Haven't tried raid 6 or 5.  Haven't tried the "SA" model that supports SAS     
The only models I've tested and recommended lately are exactly those
though.  The 9690SA is the earliest 3ware card I've mentioned as seeming
to have reasonable performance.  The 95XX cards are certainly much
slower than similar models from, say, Areca.  I've never had one of the
earlier 96XX models to test.  Now you've got me wondering what the
difference between the earlier and current 96XX models really is.   
9650 was made by 3Ware, essentially a PCIe version of the 9550. The 9690SA
was from some sort of acquisition/merger. They are not the same product line
at all.
3Ware, IIRC, has its roots in ATA and SATA RAID.


I gave up on them after the 9650 and 9550 experiences (on Linux) though. 
My experience under FreeBSD:

1. The Adaptecs suck.  1/3rd to 1/2 the performance of....
2. The 9650s 3ware boards, which under FreeBSD are quite fast.
3. However, the Areca 1680-IX is UNBELIEVABLY fast.  Ridiculously so in fact.

I have a number of 9650s in service and have been happy with them under FreeBSD.  Under Linux, however, they bite in comparison.

The Areca 1680 is not cheap.  However, it comes with out-of-band management (IP-KVM, direct SMTP and SNMP connectivity, etc) which is EXTREMELY nice, especially for colocated machines where you need a way in if things go horribly wrong.

One warning: I have had problems with the Areca under FreeBSD if you set up a passthrough (e.g. JBOD) disc, delete it from the config while running and then either accidentally touch the device nodes OR try to use FreeBSD's "camcontrol" utility to tell it to pick up driver changes.  Either is a great way to panic the machine. 

As such for RAID it's fine but use care if you need to be able to swap NON-RAID disks while the machine is operating (e.g. for backup purposes - run a dump then dismount it and pull the carrier) - it is dangerous to attempt this (the 3Ware card does NOT have this problem.)  I am trying to figure out exactly what provokes this and if I can get around it at this point (in the lab of course!)

No experience with the 9690 3Wares as of yet.

-- Karl

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