[DRBD-user] Hardware-recomendation needed

Lars Ellenberg lars.ellenberg at linbit.com
Sun Apr 1 20:20:09 CEST 2012

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.


On Sun, Apr 01, 2012 at 02:16:42PM +0200, Arnold Krille wrote:
> On Saturday 31 March 2012 15:08:59 Digimer wrote:
> > On 03/31/2012 02:25 PM, Lukas Gradl wrote:
> > > Am Freitag, den 30.03.2012, 12:15 -0700 schrieb Digimer:
> > >> Re: RAID 1; I've used these little adapters quite a bit in production
> > >> and have not had any heat problems;
> > >> 
> > >> http://usa.chenbro.com/corporatesite/products_detail.php?sku=72
> > > 
> > > Thanks for that link - they look interesting.
> > > 
> > >> SSDs are nice, but they are not enterprise class (unless you have
> > >> serious money). I'd recommend looking at 2x seagate 10k or 15k SAS
> > >> drives. Plug those into an LSI 9265-8i with BBU and you will likely find
> > >> the performance is quite nice, without inducing the risks of running
> > >> into early failure on SSDs.
> > > 
> > > 2 LSI 6295 with BBU, 4 10k SAS drives, the mounting bays - that's around
> > > 2500 EUR.
> > > 
> > > For now the system uses two local SATA-Drives with software-raid1 and
> > > this setup is more than enough performance. Is there really no cheaper
> > > solution to get DRBD up and running with the same perfomance than a
> > > local Software-Raid1?
> > I'm not sure I understand the question, sorry.
> > 
> > DRBD isn't much slower than the native disk performance, provided your
> > network is fast enough.
> 
> I wouldn't sign that. While 1GB-network compares to current sata disks, the 
> throughput isn't everything. There is also latency where the network layer in 
> drbd introduces a factor of ten compared to pure local disks and when using C-
> protocol.

How is that?

SATA disk latency for random writes: >= 10ms
Round trip time on GigE direct link: < 0.15 ms

So wherever you see your factor 10,
it is unlikely to be the "network layer in DRBD".

> And when there are many users/apps accessing this resource, its the 
> latency that makes them complain.

That is correct.


-- 
: Lars Ellenberg
: LINBIT | Your Way to High Availability
: DRBD/HA support and consulting http://www.linbit.com



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