Re: StorEdge 3310, disk sets, 2 hosts
From: noone (noone_at_noone.org)
Date: 09/25/04
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Date: Sat, 25 Sep 2004 18:04:51 +1000
Elias wrote:
> noone wrote:
>>
>> Forget about the mirroring of the arrays via disksuite for the mean time.
>>
>> Assume for the moment that there is just 1 array, the question still
>> stands:
>>
>>
>> 1) One or two controllers on the 3310
>>
>> Do I need 1 or 2 controllers ( one controller on 3310 per host ) ?
>>
>>
>> 2) Any issues of taking the controller from another 3310 and placing
>> it on my existing 3310.
>>
>>
>> 3) Finally, has any done this before and is this setup ( diskset, 2
>> hosts, NO clustering and NO HA ) supported by Sun ?
>>
>>
>
>
> The second controller does not add functionality, it only adds
> redundancy. So, there is no need to get a second controller for either
> array.
>
That's what I thought, but they were suggesting that the second
controller IS required.
> As for earlier comments about array based vs host based mirroring, in
> your current case host based mirroring is a better way to go. Any time
> you have things in one physical enclosure you have risk. By spreading
> the mirror across multiple arrays you reduce risk. There are plenty of
> instances where a single array (this is vendor neutral) that didn't have
> a single point of failure goes down. This is usually caused by bugs in
> the firmware.
>
> The type of DB failover you want to do is probably the most risky in
> terms of having a successful failover. One of the value add features of
> cluster software is the cluster file system. If you have locks or
> reservations that don't get properly released the second server may
> refuse to import the volume.
But solstice disksuite allows you to reserve the diskset forcibly in the
event that host A, which previously had the reservation, have a hardware
failure and can no longer boot for whatever reason ... so that host B
can reverse the diskset forcibly:
http://docs.sun.com/db/doc/806-3205/6jccc20rb?a=view
Doesn't that solve the problem ?
>
> There are other options though. Most of the options that have more
> reliable failovers involve replicating the data from server to server
> instead of through a mirror. This would mean that you put one 3310 on
> your 280 and one on the 220, with no array doing any multi-hosting. A
> list of things that are known to work for this are:
> - Sun Network Data Replicator
> - Oracle DataGuard
> - Veritas Volume Replicator
> - Scripted Log Shipping
>
> You should be seeing a theme here. Replicate the updates over the
> network to the standby server while it's in recovery mode and have it
> read in all the logs, or replicate the volume over the network. By
> having each server use independent storage you don't have to worry about
> importing and exporting volumes. You do have to make some decisions on
> synchronous or asynchronous replication. i.e. does the commit happen
> when both servers write the data or only when the primary server writes
> it. Your risk is transactions that haven't been sent and the ones that
> are in flight. It's all a matter of how much risk you want to take.
>
Yes I know .. we investigated the and evaluated Sybase Replication
Server ( reading transations longs from one database to applying these
transaction logs to another database ) to implement a warm-standby. It
works well ... but the licensing cost is very prohibitive for a small
company.
>
> Elias
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