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 :)
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.
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.
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.
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?
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).
I stay away from LVM because that just sucks. It wouldn´t even have any advantage
in this case.
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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