ssd caching in hp/dell server's

alexgold

Hello!
I have a couple of R620 and HP DL360 g8 servers with raid-5 1TB 15K (*4) disks.
To speed up the latency, I want to buy an SSD disk and use it as a caching disk to speed it up.

Someone here has experience with this and can explain exactly how I make that happen?

Thanks!
Alex.

jh_aurologic

I'd go with bcache. We use bcache already with 16+ storage servers, works pretty decent for nvme caching virtual machine disk images.

jackb

dm-cache / lvmcache is also a good choice.

doughnet

If possible switch to zfs and use the sss as a cache

marvel

Caching will only increase latency, since your data first has to be written to the SSD and then to the slow spinning disks.

But tbh. unless you can run these servers with free power I wouldn't bother with those machines. I would probably sell them. They are too old and with RAID-10 you net 2 TB per server which is just not worth the power they require to run, let alone doing an investment in SSD drives.

Better sell them buy a NAS with a couple of SATA disks.

soundpool

in case you're using hardware raid you can also have a look at caching options in the RAID controller itself.
On the HP(E) it's called smartcache.
Not entirely sure on the Dell, may be called cachecade or something like that.

So if you have a P420(i) in that DL360 G8, this may be an option.
Keep in mind you may have to purchase/obtain a smartcache license.
Below an overview of the HPE RAID controllers and smartcache support:
https://h20195.www2.hpe.com/v2/GetPDF.aspx/c04123148.pdf

Although lack of write-back caching support it a bit worrying, as you may not experience lower latencies because of this.

Another downside of this is that you'd need a SATA drive to cache on. (needs connection to the RC)
As mentioned earlier in this thread, with a software based option you can cache on a much faster NVMe.

@marvel said: Caching will only increase latency, since your data first has to be written to the SSD and then to the slow spinning disks.

True for write-through caching, but not necessarily for write-back.
Depending on the load fluctuation it can actually improve performance and latency.
That is of course if you don't have a high continuous load preventing the cache from being written back to the actual drives.

jsg

@marvel said:
Caching will only increase latency, since your data first has to be written to the SSD and then to the slow spinning disks.

But tbh. unless you can run these servers with free power I wouldn't bother with those machines. I would probably sell them. They are too old and with RAID-10 you net 2 TB per server which is just not worth the power they require to run, let alone doing an investment in SSD drives.

Better sell them buy a NAS with a couple of SATA disks.

Depends. 2.5" disks don't need much more el. power than SSDs (but 3.5" do). As for the system&model specific controllers I don't know, but that's not a sensible way to go anyway; main reason: the relative small size of the disks. So I'd suggest to max out the Raid controller memory and to add some system memory too and to then let the controller and the OS take care of it (with a sensible config of course).