[zfs-discuss] windows on thin provision zvol: how to force trim?

Gordan Bobic gordan.bobic at gmail.com
Tue Oct 15 09:16:11 EDT 2013


Depends on your pool layout. I use mirrored SSDs and the performance isn't
too bad. To take full advantage of deduplication on zvols it's important to
make sure that volblocksize = allocation size on the child fs. So if NTFS
block size = 4KB you should make sure that volblocksize=4KB if you are
using dedupe.

If you aren't using dedupe, there is no need to adjust it away from the
default.


On Tue, Oct 15, 2013 at 2:06 PM, Ivan Krutskikh <stein.hak at gmail.com> wrote:

> The performance on zvols with blocksize less then 64K was terrible not so
> long ago... Were there any breakthroughs?
>
>
> 2013/10/15 Gordan Bobic <gordan.bobic at gmail.com>
>
>> Sounds like more or less the exact use-case I have. Make sure your
>> volblocksize=4KB, though.
>>
>> I go one step further. My VM zvol storage is on SSDs where I have dedupe
>> enabled for the system disks. If you run the same OS (at least major
>> version) in a large number of VMs, deduplication produces some massive
>> space savings. This works out reasonably well because low latency on SSD
>> covers up for the extra seeks, and SSD is still expensive enough that
>> overall space saving roughly proportional to the number of VMs you have
>> running makes it very much worthwhile.
>>
>> Gordan
>>
>> On Tue, Oct 15, 2013 at 1:45 PM, Ivan Krutskikh <stein.hak at gmail.com>wrote:
>>
>>> Basically, I wanted to use zvols for windows diskless booting. Maybe
>>> ntfs compression would be a nice choice. I'll think about it, thanks!
>>>
>>>
>>> 2013/10/15 Gordan Bobic <gordan.bobic at gmail.com>
>>>
>>>> That's what I use on my VMs. You might also find it is better to use
>>>> compression on the client end than on the ZFS side. That way your ZFS
>>>> storage box doesn't take the CPU hit for all of the compression going
>>>> to/from the FS, plus you get less bandwidth saturation on your interconnect
>>>> between the storage and the VM. For my Windows VMs I use NTFS compression
>>>> and ZLE on the ZFS side. Just make sure that the disk scrubbing sdelete
>>>> performs isn't subject to ntfs compression or you might find that for the
>>>> purpose of the scrub your storage suddenly becomes infinite. :)
>>>>
>>>>
>>>> On Tue, Oct 15, 2013 at 1:33 PM, Ivan Krutskikh <stein.hak at gmail.com>wrote:
>>>>
>>>>> Okay, one promissing solution is to use sdelete from microsoft (
>>>>> original post http://nex7.blogspot.ru/2013/03/zvol-used-space.html),
>>>>> which would zero-out all unused space on a zvol. However, this seams
>>>>> write-intensive. I'll test this solution and report the results
>>>>>
>>>>>
>>>>> 2013/10/15 Gordan Bobic <gordan.bobic at gmail.com>
>>>>>
>>>>>> So don't overbook. If your pool gets to 100% full you are going to
>>>>>> have major performance issues due to fragmentation anyway. Filling it up
>>>>>> from 95% to 100% is likely to be so slow it'll give you ample time (days)
>>>>>> to go and delete some snapshots or similar to free up some space.
>>>>>>
>>>>>>
>>>>>> On Tue, Oct 15, 2013 at 1:12 PM, Ivan Krutskikh <stein.hak at gmail.com>wrote:
>>>>>>
>>>>>>> My concern is resilvering time for a server full of zvol's and clones
>>>>>>>
>>>>>>> I already use lz4, but once the zvol goes full 100%- It does not
>>>>>>> shink back to original, even if the data is already deleted from the
>>>>>>> filesystem
>>>>>>>
>>>>>>>
>>>>>>> 2013/10/15 Gordan Bobic <gordan.bobic at gmail.com>
>>>>>>>
>>>>>>>> I don't think they are expected to shrink. Even if the trim gets
>>>>>>>> passed to the underlying media I'm not sure if the container's size is also
>>>>>>>> expected to shrink.
>>>>>>>>
>>>>>>>> If you are concerned about space usage, enable ZLE compression and
>>>>>>>> run a cron job that zeroes out the free space inside the VMs. Or better,
>>>>>>>> don't overbook the space.
>>>>>>>>
>>>>>>>>
>>>>>>>> On Tue, Oct 15, 2013 at 12:22 PM, Ivan Krutskikh <
>>>>>>>> stein.hak at gmail.com> wrote:
>>>>>>>>
>>>>>>>>> Okay, I've googled up to DisableDeleteNotify parameter. If it
>>>>>>>>> equals 0 (which it is by default in fact), then TRIM should be up and
>>>>>>>>> running. But my zvol devices do not shring with deletion of files from
>>>>>>>>> virtual machines disks. How come?
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> 2013/10/15 Tamas Papp <tompos at martos.bme.hu>
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> On 10/15/2013 11:20 AM, Ivan Krutskikh wrote:
>>>>>>>>>> >
>>>>>>>>>> http://comments.gmane.org/gmane.os.solaris.opensolaris.zfs/35630
>>>>>>>>>> >
>>>>>>>>>> > Please, look through the original post
>>>>>>>>>> >
>>>>>>>>>>
>>>>>>>>>> Ohh, thanks.
>>>>>>>>>>
>>>>>>>>>> tamas
>>>>>>>>>>
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