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Number of FC (fibre channel) cables to connect up to DB & ESX servers

Posted on 2012-04-01
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Last Modified: 2012-04-02
The proposed MS SQL 2008 DB will be about 800MB in size.
The ESX server is expected to host 5 VMs (all Windows 2008) in it.

I've seen DB servers with 4 FC ports & some with 2 FC ports
connected.

Q1:
On what basis/criteria do we decide how many FC / fibre ports
to connect each DB & ESX host?

The SAN switch port is going to be of 4Gbps or 8Gbps (I don't
know at this moment)

Q2:
If 2 FC ports are connected (to two different fabric switches
for redundancy), are they active-passive (live-standby)
 or active-active?  For this question, I'm trying to establish
the total nett throughput (if it's active-active, then it's double
throughput)

Q3:
If multi-pathing is used for ESX, it it better to have 2 or 4
FC ports connected?

Q4:
If we're going to take full backup of the 800MB database
daily, would it help to have 4 FC ports connected to the
DB assuming I have 4x 1Gbps NIC ports connected?

Q5:
Is there such thing as setting up a separate pair of FC switches
dedicated for Backup LAN?  If this is so, then I guess 2 FC ports
of the ESX/DB server go to the FC switches (designated for
backup) & another 2 FC ports to another pair of FC switches
for storage?  Or rather most people just zone their FC switches
such that tape libraries have one zone while the storages have
separate zones?  Assume the DB & ESX hosts are not functioning
as media backup servers.
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Question by:sunhux
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by:
SelfGovern earned 280 total points
ID: 37794604
A1: To determine how many ports (and what speed you need), calculate the bandwidth you expect to need.  Add some overhead for growth.  Then double the number of ports that indicates, since you'll probably want to be able to run with no loss of performance if you lose a switch or an Fibre Channel port somewhere.

A2: Whether active/active or active/passive depends often on which storage subsystem you're using, and perhaps on your definition of active/active.  For instance -- consider a particular entry FC storage system with two controllers, where each controller "owns" certain LUNs.   The other controller can get to the data, but that second controller needs to have the first "proxy" the data for it.   So that's perhaps "active/active with some delay".

A3: If the data you need fits over one port (and will for the reasonable future), I don't see much reason to have more than two ports (remember, since you want full performance when one path fails, you need double the number of ports you would think you'd need).   If your system only needs to pull a maximum of 5Gb/second, you won't gain anything by having 32Gb/second of bandwidth.

A4: Figure your maximum bandwidth needs, and the answers will be apparent.  Oh -- make sure your disks can keep up with whatever projections you're making.   Often times the physical source disk is the slowest part of a system (by the time you factor in fragmentation, small files, contention of active processes for the disk heads, etc.)... so that 4Gb pipe may never get filled up, even during backups.

A5: Many vendors recommend a separate SAN for your backups.  I don't think you need separate switches (unless you're close to filling up the first pair)... just make sure your zoning is well thought out and correctly implemented.
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Assisted Solution

by:Duncan Meyers
Duncan Meyers earned 220 total points
ID: 37794773
Q1: Two ports are more than enough for most environments. You'd have to be generating MASSIVe amounts of throughpaut to need four ports (and I do mean massive - think upward of 800MB/sec)

Q2: Typically they operate active-active, but this depends on the multipath algorithms in use, the SAN switching fabric and the storage array. As you are talking about VMware ESX server, it's fair to say that, for vSphere 5 using round-robin multipathing, you are active-active.

Q3: Two ports is plenty - unless you have massive I/O requirements. With 5 VMs, you don't.

Q4: Sorry - is that a serious question? Assuming you can push a 1Gb NIC to 100% utilisation, you'll get 100MB/sec - so you could get your backup in 8 seconds. Across a single 8Gb FC link, you could get your backup in 1 second (this assumes all is configured appropriately).

Q5: I can't see a need for a separate backup switching fabric from what you've described. There simply isn't a need for that sort of performance judging from what you've posted.
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