[CentOS] iSCSI best practices

Reindl Harald h.reindl at thelounge.net
Mon Dec 12 18:32:06 UTC 2011



Am 12.12.2011 19:17, schrieb John R Pierce:
> On 12/12/11 6:43 AM, Digimer wrote:
>> I handle this by setting up two servers running DRBD in active/active
>> with a simple two-node red hat cluster managing a floating IP address.
>> The storage network link uses a simple Active/Passive (mode=1) bond with
>> either link go to separate switches.
> 
> DRBD with synchronous writes?  doesn't that slow things down 
> considerably? 

there is always a compromise between performance / integrity / costs

> if its asychronous, recently written data will be lost 
> on a failure.

the main question is:
how hard is it to lose some recent data by a total crash
how often happens a total crash
what costs you have for the best compromise

> proper storage appliances implement a shared cache between the master 
> and standby storage controllers so that if the master fails, the standby 
> has all data, including cached writes.   as far as I know, there's no 
> way to easily implement this with open source, its part of the secret 
> sauce of proper redundant storage.

the question is have you the budget for a high-end SAN-storage
where all components are redundant, and even if - you have to
make backups for the totally worst case

for me it took a long time to get a HP SAN Storage with two controllers
and multipath SAS-disk which i never want to miss again, but these
things are really expensive - but well, it is the best solution since
you have redundant sotrage/controllers/disks/power-supply and a maximum
perfomracne with the two dedicated CPU's and 1 GB cache per controller

but remind the costs and look how important is a zero-downtime in worst-case
in what environement, if it is only a internal-storage iand you are a small
company it is no problem to say "guys, go home, i need a day for restore backups"

if you have public customers-services it is not an option

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