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vsphere disk latencies server down

every few weeks our vsphere 5 server goes on the run.
all applications time out, vsphere client shows that disk latencies on all services go sky-high (see screenshot).
my only solution is a reboot of the physical server and restart each virtual server.
unix servers usually need a fsck in single user mode to get rid of errors.
what could be cause of these extreme latencies ?

we use vsphere 5 on a raid-5 of 6 x 500gb local sata disks.

vsphere-latencies.jpg
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Lieven Embrechts
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Lieven Embrechts
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Are the 6 SATA disks 7,200 RPM?

6 SATA disks, RAID 5 - is going to have performance issues.

How much ram in the HOST server?

How much ram is being used by guests?
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Lieven EmbrechtsAuthor Commented:
yes, 2.5 inch 7200rpm.

enough ram in server (12 of 24gb used), guests look ok for ram usage when server runs normal.

i'm not an expert on vsphere but it feels like the IO queue is overloaded somehow, and when that happens the complete vsphere environment goes on the run ...
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
It's the 7,200rpm SATA disks.

What's the server and RAID controller?
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Lieven EmbrechtsAuthor Commented:
cisco ucs c210 m2 server
lsi 6g megaraid 9261-8i - 512wc card
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Have you got the RAID cache set to 75% Write 25% Read?

On a production machine I would not use 7,200rpm disks, the IOPs would be very poor, and worse in a RAID5 configuration.
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Lieven EmbrechtsAuthor Commented:
>>Have you got the RAID cache set to 75% Write 25% Read?

if it's not default, why would i do that, where would i do that ?

>>On a production machine I would not use 7,200rpm disks, the IOPs would be very poor, and worse in a RAID5 configuration.

consultant used raid 6 i believe, he told me all IO would be distributed over the disks so better performance with raid 5 or 6.
what would be your suggestion for disks and raid-config ?

is the graphic you see (see screenshot) something seen before ? reason ?
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
SATA disks are very slow, poor performance, should only be used for Labs, Research, or Archives/Backup.

Your issues, is your poor SATA disks.

RAID 10 is faster for read and writes.

RAID Cache Configuration can be changed in the RAID BIOS.
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Paul SolovyovskyCommented:
I would agree with hanccocka, SATA drive can pose problems.  Take a look at what is happening on the guest side such as a SQL server doing maintenance work on a database.  I would also ensure that the 75% write, by default I think the UCM servers are 50/50 which can slow down the write performance and as you can see it's thw write latency you're having an issue with.  SAS drives would be preferred.
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
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Lieven EmbrechtsAuthor Commented:
had a look at the cache settins several were referring to:
apparently the lsi controller is by default full write cache, there is no read cache.
as for the sata disks, i don't see a problem with light apps & light load.

write latencies go up all of a sudden every 2 days at random time,
i need a method to find what is causing it.
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