[Linux-cluster] GFS and the Dell pv220s or iSCSI

[Alan Wood]

sorry I've been away from the list and only getting to this 1-month old 
thread now...

Brendan, I have a pv220s which I used for a GFS cluster last year with 
disasterous consequences.  Performance was terrible for multiple concurrent 
users (one of the chief thing you are worried about in selecting SCSI 
over SATA in the first place).  In addition, the support I got from Dell, 
while attentive, ended after 3 months with "we do not support using the 
pv220s in an active-active linux cluster".  This is after I had reverted 
out of GFS and was using linux-ha to do failover and getting SCSI 
reservation errors which led to data loss...

I have since moved on to iSCSI as a few people on the list suggested you 
do.  Instead of the Dell/EMC box most people were talking about I went with 
a Promise vtrak M300i.  as far as I could see there were only a couple of 
minor differences and the promise box was less than half the price when 
fully stocked with SATA drives (because Dell totally rips you off on the 
price of the drives).  It supports SATA II and NCQ.
so far performance has been just as good as with the pv220s in clustered 
config (I am only using 10K drives in the 220 though).  I have just bought 
a couple of Qlogic HBAs (in the US $500 instead of the $2K someone 
mentioned in Brazil) but have yet to test them.  I also bought a second 
enclosure and am hoping to use lvm mirroring and multipathing as soon as 
its good to go in order to have full redundancy:
http://www.redhat.com/f/summitfiles/presentation/May31/Clustering%20and%20Storage/StorageUninterrupted.pdf

btw, HP does offer an iSCSI head unit that you can then daisy-chain SCSI or 
SATA enclosures off of -- so if you really want SCSI disks that would be an 
option:
http://h18006.www1.hp.com/products/storageworks/msa1510i/index.html
I haven't tested it (and last I heard HP only officially supported it in 
Windows) but if anyone else on the list has experience with it I'd be 
curious to hear it.

now that I have a 10gig switch available to me I'm also curious to try out 
a 10gig iSCSI enclosure but haven't seen any on the market...
-alan

> ------------------------------
>
> Message: 5
> Date: Tue, 15 Aug 2006 21:29:59 +0100
> From: Brendan Heading <brendanheading at clara.co.uk>
> Subject: [Linux-cluster] Setting up a GFS cluster
> To: linux-cluster at redhat.com
> Message-ID: <44E22EC7.8020506 at clara.co.uk>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> 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
>
>
>
> ------------------------------
>
> Message: 7
> Date: Tue, 15 Aug 2006 23:23:40 -0300
> From: "Celso K. Webber" <celso at webbertek.com.br>
> Subject: Re: [Linux-cluster] Setting up a GFS cluster
> To: linux clustering <linux-cluster at redhat.com>
> Message-ID: <44E281AC.4010608 at webbertek.com.br>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> 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
>>
>> --
>> Linux-cluster mailing list
>> Linux-cluster at redhat.com
>> https://www.redhat.com/mailman/listinfo/linux-cluster
>>
>
>