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EMC SAN Very Slow
Hello
We have an EMC SAN AX150i. We have 6 VMware hosts connected to it with multiple vm's running off the SAN. Until recently we had seven 500 gb drives in the SAN using RAID5 with one hotspare. We made one large LUN that VMware uses. Everything was working fine for months. Last week I added five more 500GB drives and expanded them onto the LUN for a total of 4.5 TB. The expansion took about 8 hours to complete. During the expansion our servers were bogged down tremendously. To the point where we just had to power our VM's off. Once the expansion finished it is still bogged down. Now it's been a week since the expansion and everything is still at a crawl even after moving almost all vm's off the SAN onto local disk. And my VM hosts do not even recognize the newly expanded space. Can anyone give some insight into this? Is it possibly still expanding? Does performance die when you dedicate all space to one LUN? Can I do a reboot without affecting the data on the SAN?
Thanks in advance!
dynamox
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September 16th, 2010 12:00
VMFS does not support volumes greater than 2 TB, unless you use extents which is not all that great. Can you verify that expansion completed ?
RRR
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September 17th, 2010 01:00
500GB drives are SATA drives and therefor by far not as fast as FC drives (or SAS). If you're already hammering the SATA LUN's and start an expansion, performance can (and will in your case) be impacted. If the expansion only took 8 hours, you might have set the priority to high, which indeed WILL have a perfoermance impact. Even on FC, I almost never use the high setting. Ok, so expanding takes hours, maybe even days, but then again: (almost) no performance impact.
Oh, one other thing: please don't call a storage array a SAN, since a SAN is only the NETWORK from a host to the storage. A SAN is the Storage Area Network, so NETWORK !!! This network consists of 1 or (almost always) more switches and you need HBA's and fiber patch cables to connect each host to these switches. From each switch you again need patch cables to connect the storage array(s) to the SAN.
So:
Host ---- SAN ---- Storage Array ---- LUN