topic Re: FATA disks in RAID5 for VMware guests in Operating System - VMware

FATA disks in RAID5 for VMware guests

APT_SG — Tue, 09 Mar 2010 08:44:46 GMT

Hi All,

We are moving to the dataceneter and planning to have SQL servers (virtualized) and some Windows/Linux mixed environment .

We are considering tiered storage
on EVA4400 - FC RAID 10 for SQL databases and RAID5 across 24 FATA 1TB disks
for VMware ESX guests.guests will not be IO intensive, in total we will have about 40 vmguests.

HP is describing FATA disks as suitable for near online
storage, however I am not convinced that 24 spindles will not be enough for
running VMWare for our setup.
Does anyone has opinion on why this could
be a such a bad idea?

Thank you

Sergei

Re: FATA disks in RAID5 for VMware guests

Uwe Zessin — Tue, 09 Mar 2010 09:20:11 GMT

> will not be IO intensive

And that means, what? 1 IOPS? 10IOPS? Per VM / all VMs together? What duty cycle?

One of the problems with FATAl disk drives is that they are not meant for continuous IOs.

This year's EVA-4400 quickspecs have even started to disrecommend FATAl disk drives for CA replication targets when the source is on FC disks:

""FATA drives are designed for lower duty cycle applications such as near on-line data replication for back-up. These drives should not be used as a replacement for EVA high performance, standard duty cycle, Fibre Channel drives. Doing so could shorten the life of the drive.
FATA drives are not recommended in Continuous Access applications as the remote storage location for local data residing on standard higher speed disk drives. Continuous Access tends to perform fairly high duty cycle random writes to the remote disk array. Matching remote FATA drives with local FC drives will impact the performance of your application, and will adversely impact the reliability of the FATA drives.""

(An interesting detail as I often have to discuss this with customers who think - or get suggested by competitors - those disks are 'just slower' than FC disks and they want to use them for servers/VMs that "don't _need_ fast I/O".)

Re: FATA disks in RAID5 for VMware guests

APT_SG — Tue, 09 Mar 2010 09:25:36 GMT

Thank you,

You are absolutely right, I should have more details on IOPS..
Currently our VI is connected to CX3-10 EMC array and most logical way to measure IOPs would be to get stats from this array.Unfortunately enabling stats requires additional licensing.I believe my only choice here is running perfmon for windows and something similiar for linux, then aggregate the data.
But I believe that perfmon data can be pretty different from array data due to the caches?

Sergei