I'm giving my unraid server a revamp. Last time I built it with 5.0rc12 I had some problems with my cache drive (mover not transferring data overnight), and it turned out to be a problem with simple features that was causing it. I now have my server without a cache drive, and for the most part, albeit rather slow it does its job.

 

I have some money that I can spend on an additional data drive (I'm running close to 1 TB of remaining space on the array) or get an SSD as a cache drive. For about $100 I can buy a Crucial M500 240 GB 3.5" SSD or a 4TB 5400 RPM Hard drive.

 

My question is this: Have any of you noticed a substantial increase in data write speed using a cache drive, particularly, by using an SSD in its place? I read the following opinions on the forums:

 

1. Bottleneck to write speeds is usually the Gigabit network, not necessarily the HD speed.

 

2. An SSD does not give you a noticeable increase in speeds during read/write as a cache drive compared to a 7200 rpm spinner.

 

3. It is not a good idea to have user shares enabled in the cache drive (because of the possibility that data is unprotected during the time it resides on the cache drive before it gets moved over to the array).

 

 

The reason I ask is that currently, when I download media (movies/TV shows/music) from my home PC, I need to then manually copy it to the server, and this is a painful since the speeds I get are probably in the order of 10 MB/sec -- sometimes slower. Will adding a cache drive, and better yet and SSD for that purpose, help me speed this up?

 

If the answer is probably not, then I'd rather spend that money on buying a 4 TB hard drive that I can add to the array and maybe by myself a smaller 250-500 MB 7200 RPM spinner for the cache drive. On that same note, do you guys routinely EXCLUDE your data shares from the cache drive or is this not really a practical issue?

 

I'd appreciate any insight.

Sorry, I misread... buy the 4TB. 

 

Buy the 4TB drive.

 

However ... your write speeds are consistent with a 100Mb network - NOT Gb.  With a Gb network you should be getting in the neighborhood of 30MB/s, which is limited by UnRAID, not the network.  What you're seeing now (10MB/s) is almost certainly due to network limitations.

 

If your equipment is all Gb (adapters, router, and any switches you might have), then the slow write speeds are almost certainly due to a network cable ... if there are any discontinuities in the cable (or the connectors) then it will revert to the slower 100Mb speed, which seems to be what's happening.  Replace ALL of your Ethernet cables that are involved in the transfers.

 

If you have any smaller 1-2Tb drives in the system, I would buy a 4TB, upgrade a smaller driver and re-purpose the original into a cache.  If your moving the files from your local PC, then just keep the originals until the mover transfers them into the array.  I personally wold not use a SSD as a cache, even though it would be nice.

 

I advocate using a larger spinning drive as the cache as it allows you to use a share on the cache configured to not be moved to for other purposes.  For example, I am playing/setting up a configuration using btsync on my server to sync with a raspberry pi nas to sync data to a remote location for off site storage. 

 

Great posts, guys. Thank you!

 

This makes the decision a lot easier, I guess I should go with the 4 TB storage drive.

 

1. Would you recommend a 7200 RPM 250 GB HDD for a cache drive? My other drives are all 5400 RPM green drives that I bought when I started the server, so I don't really have fast spinner drives.

 

2. Do most people now AVOID putting shares on the cache drive? such as their <Movie> or <Music> shares so that it gets written faster (since there is no parity calculation involved), and have it moved to the main array later via the "Mover" script? I'm curious, because when I used to have a cache drive that it what I did.

 

Thanks again for all the posts. Keep 'em coming.

Sorry to point the obvious, but you do have a 4TB parity drive?

1. Would you recommend a 7200 RPM 250 GB HDD for a cache drive? My other drives are all 5400 RPM green drives that I bought when I started the server, so I don't really have fast spinner drives.

 

If you already have it sure.  I would not purchase a drive that small. 

 

CaptainSpalding asked a good question, what size is your parity drive today.

@CaptainSpalding -- Yes I have a 4 TB parity.

 

 

Sent from my iPhone using Tapatalk

As CaptainSpalding noted, you DO of course, need to have a 4TB parity drive if you're going to add a 4TB data drive to your system 

 

As for a 250GB 7200rpm cache drive -- the faster rotational speed will provide slightly better access time than a 5400 or 5900rpm drive;  but it's likely that the areal density on an older 250GB drive is much lower than the newer drives, so the transfer rate is likely better with your larger, 5400/5900rpm drives.

 

... I'd just use whatever's convenient.

 

... I'd just use whatever's convenient.

Yep. Don't overthink it.

The speed up from ANY cache drive will be welcome.

 

If your write speed doesn't markedly increase, then reexamine your network as garycase points out.

Thanks guys, actually I found a 1 TB SSHD that I had planned to use for something else lying around. I'll probably use that as the cache drive. Already ordered the 4 TB Hitachi Deskstar from B&H... Awesome!

 

Thanks again.

Thanks guys, actually I found a 1 TB SSHD that I had planned to use for something else lying around.

Dude!  Just mail me your box of spare parts! I'm happy to take the clutter off your hands