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On Sat, April 20, 2013 17:38, Jarry wrote: |
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> On 20-Apr-13 17:00, Tanstaafl wrote: |
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> |
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>> Another question - are there any caveats as to which filesystem to use |
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>> for a mail server, for virtualized systems? Ir do the same |
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>> issues/questions apply (ie, does the fact that it is virtualized not |
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>> change anything)? |
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> |
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> Problem of virtualized filesystem is not that it is virtualized, |
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> but that it is located on datastore with more virtual systems, |
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> all of them competing for the same i/o. *That* is the bottleneck. |
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> If you switch reiser for xfs or btrfs, you might win (or loose) |
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> a few %. If you optimize your esxi-datastore design, you might |
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> win much more than what you have ever dreamed of. |
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If the underlying I/O is fast enough with low seek-times and high |
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throughput, that handling multiple VMs using a lot of disk I/O |
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simultaneously isn't a problem. Provided the Host has sufficient resources |
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(think memory and dedicated CPU) to handle it. |
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> I have 8 VMs (out of them 6 are Gentoo) hosted on ESXi, intended |
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> for various tasks (mail, dns, mysql, web, etc), moderately loaded. |
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> I used hw-raid controller with 2x sata-hdd in raid1 but performance |
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> was quite dissapointing and I experienced all sorts of i/o jams. |
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Which hw-raid controller did you use? |
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RAID-1 (mirroring) isn't actually known for high performance. |
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> Then I switched hdd for ssd (yes I use 2 of them in raid1, even |
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> if this is not generally recommended) and performance rocks now! |
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> I can start now kernel compilation on all 6 VMs at the same time, |
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> with near-zero performance penalty (depending on cpu/vcpu ratio |
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> and number of threads used). Unthinkable with hdd-based datastore. |
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I have HDD-based datastores and can do this on 4 VMs (single quad-core |
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CPU) without any penalty. |
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> I would definitely recommend using SSD. Either directly as |
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> datastore for VMs, or at least as EXSi host-cache. There is |
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> also possibility of "hybrid-raid" (1xSSD and 1xHDD in raid1) |
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> on some raid-controllers. Or if your pocket is really deep, |
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> you could grab one of those FusionIO-cards to avoid being |
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> limited by rather slow sata-interface (SSD for PCIe)... |
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A decent hardware raid-controller with multiple disks running in a higher |
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raid version is cheaper then the same storage capacity in SSDs. |
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