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Re: [Linux-cluster] Setting up a GFS cluster



Hello Brendan,

Although Dell hardware is an excellent choice for Linux, the PV220S solution is terrible at performance under a cluster environment.

The reason is that the PV220S itself does not manage RAID devices, it is in fact a JBOD (Just a Bunch Of Disks). The RAID management is done by the SCSI controllers within the servers (PERC 3/DC or PERC 4/DC).

Since there is a possibility of one of the machines going down, together with data in the controller's write cache, this solution automatically disable the write cache (write through mode) when you set the controllers in "cluster mode".

The end result is very poor performance, specially on write operations. It's not uncommon that Dell provides the PV-220S with 15K RPM disks to compensate this performance penalty due to lack of write cache.

As far as I can tell, Red Hat did support the PV220S solution in the past, during the RHEL 2.1 era, but it is not supported anymore as certified shared storage for cluster solutions (RHCS or RHGFS).

If you still plan to go on, be warned that the PV220S performs better in Cluster Mode if you set up the data transfer rate to 160 MB/s instead of 320 MB/s (the PERC 3/DC supports transfer rates of up to 160 MB/s while the PERC 4/DC supports up to 320 MB/s). This is a known issue at Dell support queues.

As an extra information, there were too many problems about reliability with the PV220S when used in Cluster Mode, this can be seen by the large amount of firmware updates for the PERC 3/DC and 4/DC (LSI Logic based chipset, megaraid driver on Linux). More recent firmware versions seem to have corrected most logical drive corruption problems I've experienced, so I believe the PV220S is still worth a try if you can live with the poor performance issue.

Maybe a Dell|EMC AX-100 using iSCSI could a better choice with a not so high price tag.

Sorry for the long message, I believe this information can be useful to others.

Best regards,

Celso.

Brendan Heading escreveu:
Hi all,

I'm planning to build a cluster using a pair of PE1950s, using RHEL 3 (or 4) with RHCS. Plan at the moment is to use GFS. Most of our stuff is Dell, therefore the obvious choice is to use a Dell PowerVault 220S as the shared storage device.

Before I kick off with this idea I'd be interested to hear if anyone had any issues with this kind of setup, or if there were any general performance problems. Are there other SCSI enclosures which might be better or more appropriate for these purposes ?

Regards

Brendan

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