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VM Best Practices: Difference between revisions
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=== Maximum volumes per VM === | === Maximum volumes per VM === | ||
'''Avoid attaching more than three volumes to a VM'''. This has been observed to lead to kernel timeouts which can affect any disk operations on those volumes and may have a cascading effect, and can render the VM effectively inoperative. While using a data volume is advisable (see above), use only one and you can carve it up into multiple filesystems inside your VM, and expand it as necessary. | '''Avoid attaching more than three volumes to a VM'''. This has been observed to lead to kernel timeouts which can affect any disk operations on those volumes and may have a cascading effect, and can render the VM effectively inoperative. While using a data volume is advisable in some cases (see above), use only one and you can carve it up into multiple filesystems inside your VM, and expand it as necessary. | ||
This has been observed on Arbutus (west.cloud.computecanada.ca) by multiple users, although it may be somewhat dependent on volume size. In one case, 3 x 100GB volumes attached to a p4-6gb VM caused kernel timeouts whenever disk operations of any magnitude were attempted. It was very difficult to copy more than 500MB of data between two filesystems, for example. | This has been observed on Arbutus (west.cloud.computecanada.ca) by multiple users, although it may be somewhat dependent on volume size. In one case, 3 x 100GB volumes attached to a p4-6gb VM caused kernel timeouts whenever disk operations of any magnitude were attempted. It was very difficult to copy more than 500MB of data between two filesystems, for example. | ||
Test of a similar situation was performed on East Cloud and with 4 x 100GB data volumes (along with the root volume), the same OS and a similar VM flavour, the issue did not occur. This VM had more memory (15 GB instead of 6 GB) but high memory usage was not observed in the Arbutus case and this isn't believed to be a factor. | |||