[Users] flashcache
Pavel Odintsov
pavel.odintsov at gmail.com
Thu Jul 10 03:32:01 PDT 2014
Could you share your patches to vzmigrate and vzctl?
On Thu, Jul 10, 2014 at 2:25 PM, Pavel Odintsov
<pavel.odintsov at gmail.com> wrote:
> Thank you for your answers! It's really useful information.
>
> On Thu, Jul 10, 2014 at 2:08 PM, Pavel Snajdr <lists at snajpa.net> wrote:
>> On 07/10/2014 11:35 AM, Pavel Odintsov wrote:
>>>> Not true, IO limits are working as they should (if we're talking vzctl
>>>> set --iolimit/--iopslimit). I've kicked the ZoL guys around to add IO
>>>> accounting support, so it is there.
>>>
>>> You can share tests with us? For standard folders like simfs this
>>> limits works bad in big number of cases
>>
>> If you can give me concrete tests to run, sure, I'm curious to see if
>> you're right - then we'd have something concrete to fix :)
>>
>>>
>>>> How? ZFS doesn't have a limit on number of files (2^48 isn't a limit really)
>>>
>>> It's ok when your customer create 1 billion of small files on 10GB VPS
>>> and you will try to archive it for backup? On slow disk system it's
>>> really nightmare because a lot of disk operations which kills your
>>> I/O.
>>
>> zfs snapshot <dataset>@<snapname>
>> zfs send <dataset>@<snapname> > your-file or | ssh backuper zfs recv
>> <backupdataset>
>>
>> That's done on block level. No need to run rsync anymore, it's a lot
>> faster this way.
>>
>>>
>>>> Why? ZFS send/receive is able to do bit-by-bit identical copy of the FS,
>>>> I thought the point of migration is to don't have the CT notice any
>>>> change, I don't see why the inode numbers should change.
>>>
>>> Do you have really working zero downtime vzmigrate on ZFS?
>>
>> Nope, vzmigrate isn't zero downtime. Due to vzctl/vzmigrate not
>> supporting ZFS, we're implementing this our own way in vpsAdmin, which
>> in it's 2.0 re-implementation will go opensource under GPL.
>>
>>>
>>>> How exactly? I haven't seen a problem with any userspace software, other
>>>> than MySQL default setting to AIO (it fallbacks to older method), which
>>>> ZFS doesn't support (*yet*, they have it in their plans).
>>>
>>> I speaks about MySQL primarily. I have thousands of containers and I
>>> can tune MySQL for another mode for all customers, it's impossible.
>>
>> As I said, this is under development and will improve.
>>
>>>
>>>> L2ARC cache really smart
>>>
>>> Yep, fine, I knew. But can you account L2ARC cache usage per customer?
>>> OpenVZ can it via flag:
>>> sysctl -a|grep pagecache_isola
>>> ubc.pagecache_isolation = 0
>>
>> I can't account for caches per CT, but I didn't have any need to do so.
>>
>> L2ARC != ARC, ARC is in system RAM, L2ARC is intended to be on SSD for
>> the content of ARC that is the least significant in case of low memory -
>> it gets pushed from ARC to L2ARC.
>>
>> ARC has two primary lists of cached data - most frequently used and most
>> recently used and these two lists are divided by a boundary marking
>> which data can be pushed away in low mem situation.
>>
>> It doesn't happen like with Linux VFS cache that you're copying one big
>> file and it pushes out all of the other useful data there.
>>
>> Thanks to this distinction of MRU and MFU ARC achieves far better hitrates.
>>
>>>
>>> But one customer can eat almost all L2ARC cache and displace another
>>> customers data.
>>
>> Yes, but ZFS keeps track on what's being used, so useful data can't be
>> pushed away that easily, things naturally balance themselves due to the
>> way how ARC mechanism works.
>>
>>>
>>> I'm not agains ZFS but I'm against of usage ZFS as underlying system
>>> for containers. We caught ~100 kernel bugs with simfs on EXT4 when
>>> customers do some strange thinks.
>>
>> I haven't encountered any problems especially with vzquota disabled (no
>> need for it, ZFS has its own quotas, which never need to be recalculated
>> as with vzquota).
>>
>>>
>>> But ext4 has about few thouasands developers and the fix this issues
>>> asap but ZFS on Linux has only 3-5 developers which VERY slow.
>>> Because of this I recommends using ext4 with ploop because this
>>> solution is rock stable or ZFS with ZVOL's with ext4 because this
>>> solution if more reliable and more predictable then placing ZFS
>>> containers on ZFS volumes.
>>
>> ZFS itself is a stable and mature filesystem, it first shipped as
>> production with Solaris in 2006.
>> And it's still being developed upstream as OpenZFS, that code is shared
>> between the primary version - Illumos and the ports - FreeBSD, OS X, Linux.
>>
>> So what really needs and still is being developed is the way how ZFS is
>> run under Linux kernel, but with recent release of 0.6.3, things have
>> gotten mature enough to be used in production without any fears. Of
>> course, no software is without bugs, but I can say with absolute
>> certainty that ZFS will never eat your data, the only problem you can
>> encounter is with the memory management, which is done really
>> differently in Linux than in ZFS's original habitat - Solaris.
>>
>> /snajpa
>>
>>>
>>>
>>> On Thu, Jul 10, 2014 at 1:08 PM, Pavel Snajdr <lists at snajpa.net> wrote:
>>>> On 07/10/2014 10:34 AM, Pavel Odintsov wrote:
>>>>> Hello!
>>>>>
>>>>> You scheme is fine but you can't divide I/O load with cgroup blkio
>>>>> (ioprio/iolimit/iopslimit) between different folders but between
>>>>> different ZVOL you do.
>>>>
>>>> Not true, IO limits are working as they should (if we're talking vzctl
>>>> set --iolimit/--iopslimit). I've kicked the ZoL guys around to add IO
>>>> accounting support, so it is there.
>>>>
>>>>>
>>>>> I could imagine following problems for per folder scheme:
>>>>> 1) Can't limit number of inodes in different folders (but there are
>>>>> not an inode limit for ZFS like ext4 but bug amount of files in
>>>>> container could broke node;
>>>>
>>>> How? ZFS doesn't have a limit on number of files (2^48 isn't a limit really)
>>>>
>>>>> http://serverfault.com/questions/503658/can-you-set-inode-quotas-in-zfs)
>>>>> 2) Problems with system cache which used by all containers in HWN together
>>>>
>>>> This exactly isn't a problem, but a *HUGE* benefit, you'd need to see it
>>>> in practice :) Linux VFS cache is really dumb in comparison to ARC.
>>>> ARC's hitrates just can't be done with what linux currently offers.
>>>>
>>>>> 3) Problems with live migration because you _should_ change inode
>>>>> numbers on diffferent nodes
>>>>
>>>> Why? ZFS send/receive is able to do bit-by-bit identical copy of the FS,
>>>> I thought the point of migration is to don't have the CT notice any
>>>> change, I don't see why the inode numbers should change.
>>>>
>>>>> 4) ZFS behaviour with linux software in some cases is very STRANGE (DIRECT_IO)
>>>>
>>>> How exactly? I haven't seen a problem with any userspace software, other
>>>> than MySQL default setting to AIO (it fallbacks to older method), which
>>>> ZFS doesn't support (*yet*, they have it in their plans).
>>>>
>>>>> 5) ext4 has good support from vzctl (fsck, resize2fs)
>>>>
>>>> Yeah, but ext4 sucks big time. At least in my use-case.
>>>>
>>>> We've implemented most of vzctl create/destroy/etc. functionality in our
>>>> vpsAdmin software instead.
>>>>
>>>> Guys, can I ask you to keep your mind open instead of fighting with
>>>> pointless arguments? :) Give ZFS a try and then decide for yourselves.
>>>>
>>>> I think the community would benefit greatly if ZFS woudn't be fought as
>>>> something alien in the Linux world, which I in my experience is what
>>>> every Linux zealot I talk to about ZFS is doing.
>>>> This is just not fair. It's primarily about technology, primarily about
>>>> the best tool for the job. If we can implement something like this in
>>>> Linux but without having ties to CDDL and possibly Oracle patents, that
>>>> would be awesome, yet nobody has done such a thing yet. BTRFS is nowhere
>>>> near ZFS when it comes to running larger scale deployments and in some
>>>> regards I don't think it will ever match ZFS, just looking at the way
>>>> it's been designed.
>>>>
>>>> I'm not trying to flame here, I'm trying to open you guys to the fact,
>>>> that there really is a better alternative than you're currently seeing.
>>>> And if it has some technological drawbacks like these that you're trying
>>>> to point out, instead of pointing at them as something, which can't be
>>>> changed and thus everyone should use "your best solution(tm)", try to
>>>> think of ways how to change it for the better.
>>>>
>>>>>
>>>>> My ideas like simfs vs ploop comparison:
>>>>> http://openvz.org/images/f/f3/Ct_in_a_file.pdf
>>>>
>>>> Again, you have to see ZFS doing its magic in production under a really
>>>> heavy load, otherwise you won't understand. Any arbitrary benchmarks
>>>> I've seen show ZFS is slower than ext4, but these are not tuned for such
>>>> use cases as I'm talking about.
>>>>
>>>> /snajpa
>>>>
>>>>>
>>>>> On Thu, Jul 10, 2014 at 12:06 PM, Pavel Snajdr <lists at snajpa.net> wrote:
>>>>>> On 07/09/2014 06:58 PM, Kir Kolyshkin wrote:
>>>>>>> On 07/08/2014 11:54 PM, Pavel Snajdr wrote:
>>>>>>>> On 07/08/2014 07:52 PM, Scott Dowdle wrote:
>>>>>>>>> Greetings,
>>>>>>>>>
>>>>>>>>> ----- Original Message -----
>>>>>>>>>> (offtopic) We can not use ZFS. Unfortunately, NAS with something like
>>>>>>>>>> Nexenta is to expensive for us.
>>>>>>>>> From what I've gathered from a few presentations, ZFS on Linux (http://zfsonlinux.org/) is as stable but more performant than it is on the OpenSolaris forks... so you can build your own if you can spare the people to learn the best practices.
>>>>>>>>>
>>>>>>>>> I don't have a use for ZFS myself so I'm not really advocating it.
>>>>>>>>>
>>>>>>>>> TYL,
>>>>>>>>>
>>>>>>>> Hi all,
>>>>>>>>
>>>>>>>> we run tens of OpenVZ nodes (bigger boxes, 256G RAM, 12cores+, 90 CTs at
>>>>>>>> least). We've used to run ext4+flashcache, but ext4 has proven to be a
>>>>>>>> bottleneck. That was the primary motivation behind ploop as far as I know.
>>>>>>>>
>>>>>>>> We've switched to ZFS on Linux around the time Ploop was announced and I
>>>>>>>> didn't have second thoughts since. ZFS really *is* in my experience the
>>>>>>>> best filesystem there is at the moment for this kind of deployment -
>>>>>>>> especially if you use dedicated SSDs for ZIL and L2ARC, although the
>>>>>>>> latter is less important. You will know what I'm talking about when you
>>>>>>>> try this on boxes with lots of CTs doing LAMP load - databases and their
>>>>>>>> synchronous writes are the real problem, which ZFS with dedicated ZIL
>>>>>>>> device solves.
>>>>>>>>
>>>>>>>> Also there is the ARC caching, which is smarter then linux VFS cache -
>>>>>>>> we're able to achieve about 99% of hitrate at about 99% of the time,
>>>>>>>> even under high loads.
>>>>>>>>
>>>>>>>> Having said all that, I recommend everyone to give ZFS a chance, but I'm
>>>>>>>> aware this is yet another out-of-mainline code and that doesn't suit
>>>>>>>> everyone that well.
>>>>>>>>
>>>>>>>
>>>>>>> Are you using per-container ZVOL or something else?
>>>>>>
>>>>>> That would mean I'd need to do another filesystem on top of ZFS, which
>>>>>> would in turn mean I'd add another unnecessary layer of indirection. ZFS
>>>>>> is a pooled storage like BTRFS is, we're giving one dataset to each
>>>>>> container.
>>>>>>
>>>>>> vzctl tries to move the VE_PRIVATE folder around, so we had to add one
>>>>>> more directory to put the VE_PRIVATE data into (see the first ls).
>>>>>>
>>>>>> Example from production:
>>>>>>
>>>>>> [root at node2.prg.vpsfree.cz]
>>>>>> ~ # zpool status vz
>>>>>> pool: vz
>>>>>> state: ONLINE
>>>>>> scan: scrub repaired 0 in 1h24m with 0 errors on Tue Jul 8 16:22:17 2014
>>>>>> config:
>>>>>>
>>>>>> NAME STATE READ WRITE CKSUM
>>>>>> vz ONLINE 0 0 0
>>>>>> mirror-0 ONLINE 0 0 0
>>>>>> sda ONLINE 0 0 0
>>>>>> sdb ONLINE 0 0 0
>>>>>> mirror-1 ONLINE 0 0 0
>>>>>> sde ONLINE 0 0 0
>>>>>> sdf ONLINE 0 0 0
>>>>>> mirror-2 ONLINE 0 0 0
>>>>>> sdg ONLINE 0 0 0
>>>>>> sdh ONLINE 0 0 0
>>>>>> logs
>>>>>> mirror-3 ONLINE 0 0 0
>>>>>> sdc3 ONLINE 0 0 0
>>>>>> sdd3 ONLINE 0 0 0
>>>>>> cache
>>>>>> sdc5 ONLINE 0 0 0
>>>>>> sdd5 ONLINE 0 0 0
>>>>>>
>>>>>> errors: No known data errors
>>>>>>
>>>>>> [root at node2.prg.vpsfree.cz]
>>>>>> ~ # zfs list
>>>>>> NAME USED AVAIL REFER MOUNTPOINT
>>>>>> vz 432G 2.25T 36K /vz
>>>>>> vz/private 427G 2.25T 111K /vz/private
>>>>>> vz/private/101 17.7G 42.3G 17.7G /vz/private/101
>>>>>> <snip>
>>>>>> vz/root 104K 2.25T 104K /vz/root
>>>>>> vz/template 5.38G 2.25T 5.38G /vz/template
>>>>>>
>>>>>> [root at node2.prg.vpsfree.cz]
>>>>>> ~ # zfs get compressratio vz/private/101
>>>>>> NAME PROPERTY VALUE SOURCE
>>>>>> vz/private/101 compressratio 1.38x -
>>>>>>
>>>>>> [root at node2.prg.vpsfree.cz]
>>>>>> ~ # ls /vz/private/101
>>>>>> private
>>>>>>
>>>>>> [root at node2.prg.vpsfree.cz]
>>>>>> ~ # ls /vz/private/101/private/
>>>>>> aquota.group aquota.user b bin boot dev etc git home lib
>>>>>> <snip>
>>>>>>
>>>>>> [root at node2.prg.vpsfree.cz]
>>>>>> ~ # cat /etc/vz/conf/101.conf | grep -P "PRIVATE|ROOT"
>>>>>> VE_ROOT="/vz/root/101"
>>>>>> VE_PRIVATE="/vz/private/101/private"
>>>>>>
>>>>>>
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>>>>>
>>>>
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>
> --
> Sincerely yours, Pavel Odintsov
--
Sincerely yours, Pavel Odintsov
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