Optimcache on Raid 0 SSDs ?

[clm]

Hello,

I initially understood that optimcache was to just decrease the memory used but now Im beginning to understand that it also will increase disk read speeds.

If I were to add two SSDs for this, would it be a good idea to put them in Raid 0 ?

Would this turn the SSDs into a cache system that uses both memory and ssds to improve read speed, a bit like an improved system that apple uses for their fusion drive except only for reads ?

[iseletsk]

Richard,

It would work that way, but only for files that don change. It wouldn help with database reads, but it would help with reads related to html, js, images, php, etc..

[clm]

Thanks,

Would it slow down database reads (having to wait for the cache to be written) ?

Would it cause any issues with software like R1Soft ? (I presume not as R1SOft reads fr om the disk not from the cache).

Would Raid 0 be an overkill ?

For things like cPanel backups, would the cache keep things like e-mails in cache and make backups much faster by removing the need to read them from disk during backup time ?

If I had a raid 0 I would probably go with 300 GB SSDs so that would be 600 GB disk space, I presume this would be enough ? I also presume disk reliability is not an issue here as there would only be cached data. What would happen if the partition wh ere the cache was stored stopped existing (removed by hardware raid) would it crash the server ?

[iseletsk]

It would not slow down database reads -- they would not be part of the cache.
It would not interfere with r1soft
for optimumcache -> I would say so.
It will not keep things like email in the cache. They are read only 2-3 times, it is just not worth it.
The partition size should really depend on your total customers file size. So it is hard to say if 600GB is a lot -- but it sounds like it is.
And no, it shouldn crash the server if that partition would become unavailable

[sqh]

In my opinion, since SSD drives are generally less reliable than HDD, I would put them in Raid1 so that if one fails, the server will keep running. In your Raid0, when one drive fails, your server is down until you can replace the drive and then get your backups from R1Soft. I do not think your customers would be pleased with that amount of downtime. I do not know why you would need 600GB of SSD space anyway. Id put the MySQL partition on the SSD, and perhaps your optimumcache directory there as well. That should be very fine with 300GB (and probably way less)

Just my opinion... your mileage may vary.

- Scott

[iseletsk]

It is a cache, so if drive fails -- no data will get lost.

[clm]

Thanks Igor, I guess I would have to test putting optimumcache on our existing ssds to try.

Scott, we are talking about cache drives and not data drives so there would be nothing to restore, just the cache to rebuild.

In my experience good quality SSDs actually fail alot less then hard drives as they have no moving parts. We have plently of hard dives that fail but so far no ssds and our datacenter also says that SSDs are more reliable.

We currently use Intel SSDs in Raid 1 for the operating system and for databases.

[sqh]

Ah, makes good sense! And thanks for the real world experience on the SSDs. That is good to know! Its contrary to things I have read, and do not have enough long term experience with them to have my own opinion.

- Scott

[clm]

There defenety are some bad series of SSDs and some brands are more reliable than others. Our datacentre uses Intels for their professional range and Samasungs for their gameserver range. Im personally got a samsung in my iMac and my other hard drive (seagate) that I installed at the same time as my SSD has already failed but the SSD is still going strong.

SSDs will start to fail after a certain quantity of writes, in tests Ive seen they tend to start failing after writhing between 600 and 700 TB of data. Im quite sure our SSDs don write 50TB of data a year maybe much less. This gives us a 12 year span before expecting a drive failure due to too many writes and even then smart errors will appear before this happens giving us time to replace them.