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I have server with RHEL 6 with Apache 2.2.22 and NFS client (nfs-utils-1.2.3),and access NFS server on private network.

My problem When the number of files increases my web site becomes slow and suffer from high CPU load.

What are the advantages or disadvantages with using SAN Storage vs NFS in this scenario?


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closed as not constructive by Chopper3, Dave M, Michael Hampton, Ward, EEAA Apr 15 '13 at 2:18

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NFS is, or can be, a SAN - so you have an issue with definitions.

Certainly a 1Gbps NFS storage solution used over a network shared with other traffic is likely to be slower than a dedicated 10/40/100Gbps FCoE network, but then again you can run NFS at those speeds and over a dedicated network. So it all comes down to what you actually have versus what you could have given budget etc.

Now you say you have 'high CPU load' - is that actually high CPU load or high process waits while the storage catches up? If you have genuinely high CPU load then faster storage may help but is far from certain to.

Basically you're going to have to come back to us with a LOT more details than you have now to get a concrete answer, anything else would be pure speculation.

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I have 2 dedicated servers connected with each others using private network,and uplink 100mbps network,and I have high CPU load "CRITICAL - load average: 148.64, 79.04, 35.13" increases when read from mount folder, and I went to know if SAN storage reading a faster and better ? – user161834 Apr 14 '13 at 11:42
Certainly running NFS over 100Mbps is very old school - consider upgrading soon. – Chopper3 Apr 14 '13 at 16:17

Generally SAN refers to a dedicated network for storage, block level

NFS/CIFS uses TCP/UDP and offers file level access

iSCSI is an TCP protocol (routeable but probably shouldn't be routed)

FC doesn't follow OSI model and needs FC networking devices (FC switch, FC HBA)

FCoE uses lower layers of Ethernet but doesn't use IP (FCoE switches like Cisco Nexus and CNA(HBA+NIC))

In order to share access on block level storage, a cluster aware file system has to be used (to handle conflicts, locking)

With SAN dedicated hardware handles I/O requests (to some degree) so it's less pressure on the CPU. You can use iSCSI with almost no investment in hardware. Be aware that NIC iSCSI offload may require a licence (Broadcom).

SAN supports multipathing. Or you can probably use layer 2 link aggregation (NIC and switch support required). 100Mbps link is far from enough for storage. I would suggest at least 2x1Gbps links. Congested links can greatly degrade storage performance. Use a dedicated VLAN or (dumb) switch for iSCSI to ensure performance and ease troubleshooting.

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Maybe obvious but... The difference between SAN and NAS (NFS) is that NFS allows you to share the same file system over the network, while SAN allows you to access a block storage over the network:

NFS: network->file system->block device
SAN: file-system->network->block device

If you don't need to share storage, SAN can be a solution, but you need a dedicated ( and special) network for good performance. If you have NFS already in place - try to optimize it. I will suggest to try following:

  • try mount with vers=3
  • try to increase acregmin and acregmax if files anew not changing too often
  • try to enable fsc (FsCache)

Of course you have to check that NFS server if not under the load by other clients.

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