[CentOS] OT: Suggestions for RAID HW for 2SATA drivesin DellPowerEdge SC

Fri Aug 31 16:15:45 UTC 2007
Ross S. W. Walker <rwalker at medallion.com>

From: centos-bounces at centos.org 
[mailto:centos-bounces at centos.org] On Behalf Of Feizhou
> 
> >> Another route you can go is getting a PCI/PCIe/PCI-X BBU 
> >> RAM/NVRAM card 
> >> to put an external journal on to speed up fsync performance for 
> >> filesystems like ext3 over software raid since these cards 
> >> can go beyond 
> >> 1GB of memory unlike hardware raid cards that usually max out 
> >> at 256MB.
> > 
> > What are some of these BBU NVRAM cards that I keep hearing people
> > talk about? I would love to check them out.
> 
> http://www.umem.com/Umem_NVRAM_Cards.html
> http://www.gigabyte.com.tw/Products/Storage/Products_Overview.
> aspx?ProductID=2180
> 
> Weird...I thought the umem cards were more than just BBU 
> SDRAM but...hmm...

Thanks, I'll have to give those bad boys a look-at.

> > 
> >> Software RAID is also good if you need to be able to transfer 
> >> the disks 
> >> to another box that does not have a hardware raid controller 
> >> or the same 
> >> controller.
> >>
> >> Weigh these in your decision. :-)
> > 
> > For 2 SATA hard disks used for the OS I think HW RAID is overkill.
> 
> Depends. HW RAID + BBU CACHE vs SW RAID vs SW RAID + 
> NVRAM...You cannot 
> say overkill in certain cases.

I only say that because if one is really looking for high performance
then more spindles then 2 will be the first thing to do and getting
that data off the OS drives that may do swap under load is key too.

> > 
> > Besides I do not believe the PERC 5IR has BBU cache, that
> > controller is really only meant as a simple RAID1 controller for
> > the OS.
> 
> Dell certainly has a BBU cache option, not sure if OP's Poweredge box 
> has that option.

Oh yes, the PERC 5e is very good, I have a couple here and they really
do pull in impressive numbers even with only 256MB write-back, I of
course use these with the MD1000 enclosures though.

> > 
> > If you use HW RAID you will need to install the manufacturer's
> > software for monitoring it for a hard disk failure.
> 
> Yes, likely a negative but with Dell supporting Linux maybe not so.

Ah, well a lot of these are Java apps for cross-platform compatibility
and some times the JavaVMs leak memory... so definitely YMMV.

> > 
> > If you wanted to add additional storage, say a SAS/SATA enclosure
> > of 15 disks, then I would definitely invest in a HW RAID card for
> > that!
> > 
> 
> Depends :-D. How many hardware RAID cards offer 1GB of cache?

Not many I can tell you that, but then again a well implemented
write-back cache doesn't need a huge amount of memory to be effective.

-Ross

______________________________________________________________________
This e-mail, and any attachments thereto, is intended only for use by
the addressee(s) named herein and may contain legally privileged
and/or confidential information. If you are not the intended recipient
of this e-mail, you are hereby notified that any dissemination,
distribution or copying of this e-mail, and any attachments thereto,
is strictly prohibited. If you have received this e-mail in error,
please immediately notify the sender and permanently delete the
original and any copy or printout thereof.