[one-users] File system performance testing suite tailored to OpenNebula

Wed Sep 11 06:55:09 PDT 2013

Not a simple answer, however this article by LE and Huang provide quite some details:
https://www.usenix.org/legacy/event/fast12/tech/full_papers/Le.pdf
we ended up using ext4 and xfs mainly, with btrfs for mirrored disks or for very slow rotational media.
Raw is good if you are able to map disks directly and you don't change them, but our results find that the difference is not that great- but the inconvenience is major :-)
When using kvm and virtio, the actual loss in IO performance is not very high for the majority of workloads. Windows is a separate issue- ntfs has very poor performance on small blocks for sparse writes, and this tends to increase the apparent inefficiency of kvm.
Actually, using the virtio device drivers the penalty is very small for most workloads; we tested a windows7 machine both as native (physical) and virtualized using a simple crystalmark test, and we found that using virtio the 4k random io write test is just 15% slower, while the sequential ones are much faster virtualized (thanks to the linux native page cache).
We use for the intensive io workloads a combination of a single ssd plus one or more rotative disks, combined using enhanceio.
We observed an increase of the available IOPS for random write (especially important for database servers, AD machines...) of 8 times using consumer-grade ssds.
cheers,
Carlo Daffara
cloudweavers

----- Messaggio originale -----
Da: "João Pagaime" <joao.pagaime at gmail.com>
A: users at lists.opennebula.org
Inviato: Mercoledì, 11 settembre 2013 15:20:19
Oggetto: Re: [one-users] File system performance testing suite tailored to OpenNebula

Hello all,

the topic is very interesting

I wonder if anyone could answer this:

what is the penalty of using a file-system on top of a file-system? that 
is what happens when the VM disk is a regular file on the hypervisor's 
filesystem. I mean: the VM has its own file-system and then the 
hypervisor maps that vm-disk on a regular file on another filesystem 
(the hypervisor filesystem). Thus the file-system on top of a 
file-system issue

putting the question the other way around: what is the benefit of using 
raw disk-device (local disk, LVM, iSCSI, ...) as an open-nebula datastore?

didn't test this but I feel the benefit should be substantial

anyway simple bonnie++ tests within a VM show heavy penalties, comparing 
test running in  the VM and outside (directly on the hipervisor).  That 
isn't of course an opennebula related performance issue, but a more 
general technology challenge

best regards,
João

Em 11-09-2013 13:10, Gerry O'Brien escreveu:
> Hi Carlo,
>
>   Thanks for the reply. I should really look at XFS for the 
> replication and performance.
>
>   Do you have any thoughts on my second questions about qcow2 copies 
> form /datastores/1 to /datastores/0 in a single filesystem?
>
>         Regards,
>           Gerry
>
>
> On 11/09/2013 12:53, Carlo Daffara wrote:
>> It's difficult to provide an indication of what a typical workload 
>> may be, as it depends greatly on the
>> I/O properties of the VM that run inside (we found that the 
>> "internal" load of OpenNebula itself to be basically negligible).
>> For example, if you have lots of sequential I/O heavy VMs you may get 
>> benefits from one kind, while transactional and random I/O VMs may be 
>> more suitably served by other file systems.
>> We tend to use fio for benchmarks (http://freecode.com/projects/fio) 
>> that is included in most linux distributions; it provides for 
>> flexible selection of read-vs-write patterns, can select different 
>> probability distributions and includes a few common presets (like 
>> file server, mail server etc.)
>> Selecting the bottom file system for the store is thus extremely 
>> depending on application, feature and load. For example, we use in 
>> some configurations BTRFS with compression (slow rotative devices, 
>> especially when there are several of them in parallel), in other we 
>> use ext4 (good, all-around balanced) and in other XFS. For example 
>> XFS supports filesystem replication in a way similar to that of zfs 
>> (not as sofisticated, though), excellent performance for multiple 
>> parallel I/O operations.
>> ZFS in our tests tend to be extremely slow outside of a few "sweet 
>> spots"; a fact confirmed by external benchmarks like this one:
>> http://www.phoronix.com/scan.php?page=article&item=zfs_linux_062&num=3 We 
>> tried it (and we continue to do so, both for the FUSE and native 
>> kernel version) but for the moment the performance hit is excessive 
>> despite the nice feature set. BTRFS continue to improve nicely, and a 
>> set of patches to implement send/receive like ZFS are here: 
>> https://btrfs.wiki.kernel.org/index.php/Design_notes_on_Send/Receive 
>> but it is still marked as experimental.
>>
>> I personally *love* ZFS, and the feature set is unparalleled. 
>> Unfortunately, the poor license choice means that it never got the 
>> kind of hammering and tuning that other linux kernel filesystem can get.
>> regards,
>> carlo daffara
>> cloudweavers
>>
>> ----- Messaggio originale -----
>> Da: "Gerry O'Brien" <gerry at scss.tcd.ie>
>> A: "Users OpenNebula" <users at lists.opennebula.org>
>> Inviato: Mercoledì, 11 settembre 2013 13:16:52
>> Oggetto: [one-users] File system performance testing suite tailored 
>> to    OpenNebula
>>
>> Hi,
>>
>>       Are there any recommendations for a file system performance 
>> testing
>> suite tailored to OpenNebula typical workloads? I would like to compare
>> the performance of zfs v. ext4. One of the reasons for considering zfs
>> is that it allows replication to a remote site using snapshot streaming.
>> Normal nightly backups, using something like rsync, are not suitable for
>> virtual machine images where a single block change means the whole image
>> has to be copied. The amount of change is to great.
>>
>>       On a related issue, does it make sense to have datastores 0 and 1
>> in a single files system so that the instantiations of non-persistent
>> images does not require a copy from one file system to another? I have
>> in mind the case where the original image is a qcow2 image.
>>
>>           Regards,
>>               Gerry
>>
>
>

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