[CentOS] cyrus spool on btrfs?

Fri Sep 8 14:57:15 UTC 2017

On 09/08/2017 09:49 AM, hw wrote:
> Mark Haney wrote:
>> I hate top posting, but since you've got two items I want to comment 
>> on, I'll suck it up for now.
>
> I do, too, yet sometimes it´s reasonable.  I also hate it when the lines
> are too long :)
>
I'm afraid you'll have to live with it a bit longer.  Sorry.
>> Having SSDs alone will give you great performance regardless of 
>> filesystem.
>
> It depends, i. e. I can´t tell how these SSDs would behave if large 
> amounts of
> data would be written and/or read to/from them over extended periods 
> of time because
> I haven´t tested that.  That isn´t the application, anyway.

If your I/O is going to be heavy (and you've not mentioned expected 
traffic, so we can only go on what little we glean from your posts), 
then SSDs will likely start having issues sooner than a mechanical drive 
might.  (Though, YMMV.)  As I've said, we process 600 million messages a 
month, on primary SSDs in a VMWare cluster, with mechanical storage for 
older, archived user mail.  Archived, may not be exactly correct, but 
the context should be clear.

>
>> BTRFS isn't going to impact I/O any more significantly than, say, XFS.
>
> But mdadm does, the impact is severe.  I know there are ppl saying 
> otherwise,
> but I´ve seen the impact myself, and I definitely don´t want it on that
> particular server because it would likely interfere with other 
> services.  I don´t
> know if the software RAID of btrfs is better in that or not, though, 
> but I´m
> seeing btrfs on SSDs being fast, and testing with the particular 
> application has
> shown a speedup of factor 20--30.
I never said anything about MD RAID.  I trust that about as far as I 
could throw it.  And having had 5 surgeries on my throwing shoulder 
wouldn't be far.
>
> That is the crucial improvement.  If the hardware RAID delivers that, 
> I´ll use
> that and probably remove the SSDs from the machine as it wouldn´t even 
> make sense
> to put temporary data onto them because that would involve software RAID.
Again, if the idea is to have fast primary storage, there are pretty 
large SSDs available now and I've hardware RAIDED SSDs before without 
trouble, though not for any heavy lifting, it's my test servers at home. 
Without an idea of the expected mail traffic, this is all speculation.
>
>> It does have serious stability/data integrity issues that XFS doesn't 
>> have.  There's no reason not to use SSDs for storage of immediate 
>> data and mechanical drives for archival data storage.
>>
>> As for VMs we run a huge Zimbra cluster in VMs on VPC with large 
>> primary SSD volumes and even larger (and slower) secondary volumes 
>> for archived mail.  It's all CentOS 6 and works very well.  We 
>> process 600 million emails a month on that virtual cluster.  All EXT4 
>> inside LVM.
>
> Do you use hardware RAID with SSDs?
We do not here where I work, but that was setup LONG before I arrived.
>
>> I can't tell you what to do, but it seems to me you're viewing your 
>> setup from a narrow SSD/BTRFS standpoint.  Lots of ways to skin that 
>> cat.
>
> That´s because I do not store data on a single disk, without 
> redundancy, and
> the SSDs I have are not suitable for hardware RAID.  So what else is 
> there but
> either md-RAID or btrfs when I do not want to use ZFS?  I also do not 
> want to
> use md-RAID, hence only btrfs remains.  I also like to use 
> sub-volumes, though
> that isn´t a requirement (because I can use directories instead and 
> loose the
> ability to make snapshots).

If the SSDs you have aren't suitable for hardware RAID, then they aren't 
good for production level mail spools, IMHO.  I mean, you're talking 
like you're expecting a metric buttload of mail traffic, so it stands to 
reason you'll need really beefy hardware.  I don't think you can do what 
you seem to need on budget hardware. Personally, and solely based on 
this thread alone, if I was building this in-house, I'd get a decent 
server cluster together and build a FC or iSCSI SAN to a Nimble storage 
array with Flash/SSD front ends and large HDDs in the back end.  This 
solves virtually all your problems.  The servers will have tiny SSD boot 
drives (which I prefer over booting from the SAN) and then everything 
else gets handled by the storage back-end.

In effect this is how our mail servers are setup here.  And they are 
virtual.
>
> I stay away from LVM because that just sucks.  It wouldn´t even have 
> any advantage
> in this case.
LVM is a joke.  It's always been something I've avoided like the plague.

>
>
>>
>>
>> On 09/08/2017 08:07 AM, hw wrote:
>>>
>>> PS:
>>>
>>> What kind of storage solutions do people use for cyrus mail spools?  
>>> Apparently
>>> you can not use remote storage, at least not NFS.  That even makes 
>>> it difficult
>>> to use a VM due to limitations of available disk space.
>>>
>>> I´m reluctant to use btrfs, but there doesn´t seem to be any 
>>> reasonable alternative.
>>>
>>>
>>> hw wrote:
>>>> Mark Haney wrote:
>>>>> On 09/07/2017 01:57 PM, hw wrote:
>>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> is there anything that speaks against putting a cyrus mail spool 
>>>>>> onto a
>>>>>> btrfs subvolume?
>>>>>>
>>>>> I might be the lone voice on this, but I refuse to use btrfs for 
>>>>> anything, much less a mail spool. I used it in production on DB 
>>>>> and Web servers and fought corruption issues and scrubs hanging 
>>>>> the system more times than I can count.  (This was within the last 
>>>>> 24 months.)  I was told by certain mailing lists, that btrfs isn't 
>>>>> considered production level.  So, I scrapped the lot, went to xfs 
>>>>> and haven't had a problem since.
>>>>>
>>>>> I'm not sure why you'd want your mail spool on a filesystem and 
>>>>> seems to hate being hammered with reads/writes. Personally, on all 
>>>>> my mail spools, I use XFS or EXT4.  OUr servers here handle 
>>>>> 600million messages a month without trouble on those filesystems.
>>>>>
>>>>> Just my $0.02.
>>>>
>>>> Btrfs appears rather useful because the disks are SSDs, because it
>>>> allows me to create subvolumes and because it handles SSDs nicely.
>>>> Unfortunately, the SSDs are not suited for hardware RAID.
>>>>
>>>> The only alternative I know is xfs or ext4 on mdadm and no subvolumes,
>>>> and md RAID has severe performance penalties which I´m not willing to
>>>> afford.
>>>>
>>>> Part of the data I plan to store on these SSDs greatly benefits from
>>>> the low latency, making things about 20--30 times faster for an 
>>>> important
>>>> application.
>>>>
>>>> So what should I do?
>>
>>
>
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-- 
Mark Haney
Network Engineer at NeoNova
919-460-3330 option 1
mark.haney at neonova.net
www.neonova.net