Stupid me forgot half of what I wanted to write:
On 11.02.2017 16:15, Thorsten Leemhuis wrote:
Lo! You afaics want to configure the hdd as "writemostly".
Google for
the term in combination with "linux" or "mdadm". It'll lead to
pages
like this:
http://tansi.info/hybrid/
http://hatim.eu/2014/05/25/leveraging-ssd-ephemeral-disks-in-ec2-part-2/
I forgot to write here: Some of those links will show that others (just
like you and me) found that writemostly doesn't work that well. I had
similar results and stopped using it. Iirc upstream added it as a quick
hack that in the end didn't work that well, so it hasn't a high priority
there and it's a known problem. Got that impression after reading some
mails in the archives when I was looking into writemostly a year or two
ago, but can't find those right now :-/
CU, knurd
> P.S.: I considered not answering the question, because it afaics and
> imho is off topic here (hence a answer only encourages people to send
> more questions like this), as the question is not specific to Fedora in
> any way. But this list is for "*Fedora kernel development*. This list is
> used for discussion of changes to the Fedora kernel that aren't
> necessarily relevant to the upstream kernel list. […]" (quote from
>
https://lists.fedoraproject.org/admin/lists/kernel.lists.fedoraproject.org/
> ) Hence I think you should send questions like that to a more general
> Linux kernel mailing list in the future. But as I said: That just my option.
>
> On 11.02.2017 15:16, Reindl Harald wrote:
>> /dev/sda: Samsung SSD 850 EVO 2TB
>> /dev/sdb: Samsung SSD 850 EVO 2TB
>> /dev/sdc: ST2000DX002-2DV164
>> /dev/sdd: ST2000DX002-2DV164
>>
>> normally i would expect that for heavy read-IO the two HDD drives would
>> sleep and the two SSD working more or less like a RAID0 but as example
>> running a btrfs-srub within a virtual machine on a 1.5 TB vdisk you can
>> hear the rotating disks clearly and there are also unexpected lags while
>> a disk IO auf around 700 MB/sec shows that it's basicly working
>>
>> pretty sure the lags are coming because read-access is also spread to
>> HDD - why is that?
>>
>> /dev/md2:
>> Version : 1.1
>> Creation Time : Wed Jun 8 13:10:56 2011
>> Raid Level : raid10
>> Array Size : 3875222528 (3695.70 GiB 3968.23 GB)
>> Used Dev Size : 1937611264 (1847.85 GiB 1984.11 GB)
>> Raid Devices : 4
>> Total Devices : 4
>> Persistence : Superblock is persistent
>>
>> Intent Bitmap : Internal
>>
>> Update Time : Sat Feb 11 15:10:31 2017
>> State : active
>> Active Devices : 4
>> Working Devices : 4
>> Failed Devices : 0
>> Spare Devices : 0
>>
>> Layout : near=2
>> Chunk Size : 512K
>>
>> Name : localhost.localdomain:2 (local to host
>> localhost.localdomain)
>> UUID : ea253255:cb915401:f32794ad:ce0fe396
>> Events : 1818029
>>
>> Number Major Minor RaidDevice State
>> 4 8 35 0 active sync set-A writemostly
>> /dev/sdc3
>> 5 8 19 1 active sync set-B /dev/sdb3
>> 7 8 51 2 active sync set-A writemostly
>> /dev/sdd3
>> 6 8 3 3 active sync set-B /dev/sda3
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