RAID5 with SSD Cache

Hi Together,

for me 4 new hdd (4tb wd red plus), want to use a raid 5 system.

Additional it got an 250gb ssd in the system which I don't use for anything. So my idea was to use this ssd as cache for the raid 5.

Before I used madam for the raid. But If I read it right in the internet, mdadm is not supporting this feature.

So far I found out that LVM ist support the ssd cache with dm-cache.

Did anyone already use this setup in production and give me some advice?

Btrfs is not an option because there is no stable support for RAID5.

Cheers Robert

HannesJo the write hole is not a big problem for me.

In the past I used mdadm without any bigger problem. Also I don't have a ups running.

But also at the btrfs is raid5 also marked as unstable. That is the reason why I don't want to use it.

As far as I read in the internet ist the lvm raid not a good performing solution.

And also there are some information that under lvm raid is also an mdadm working.

I found some benchmarking from a German guy but the most problem here is that you don't know when the test was done.

So with some further code changes it can be that the performance is not problem anymore.

How knows?

I also found some solutions where the guys use first the mdadm raid and then they used lvm.

But there is a also a raid ssd for the caching used.

At the moment I think I will not use the ssd cache option. I will start with an mdadm raid5.

But any suggestion for the filesystem? Ext4 or anything else?

Cheers Robert

Zitat von HannesJo

But as far as I can see*, the unstable flag for btrfs raid5 relies on write hole only.

* https://btrfs.wiki.kernel.org/index.php/Statu

There is an other point which makes me a little bit confused:

Some fixes went to 4.12, namely scrub and auto-repair fixes. Feature marked as mostly OK for now.