SSD Cache Drive Question


Chrisx510

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Now that my unRAID server is up and running and I'm almost done transferring files. I am going to install a left over 2TB drive as a Cache drive. First I have a few questions..

 

1. Will a SSD Cache give me faster transfer speeds?

 

2. If I rip a Blu-Ray over my network directly into unRAID instead of ripping directly to my PC and then transferring it to unRAID.. Will I get faster transfer speeds with a SSD?

 

3. What happens if you fill up your Cache drive? Are you just unable to transfer anymore data?

 

Here is the SSD I am looking into.

 

http://www.amazon.com/gp/product/B004W2JKZI/ref=s9_simh_gw_p147_d0_g147_i1?pf_rd_m=ATVPDKIKX0DER&pf_rd_s=center-2&pf_rd_r=1NZD96VATPV6GK6KFRF1&pf_rd_t=101&pf_rd_p=470938631&pf_rd_i=507846

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any decent spinner drive (mine is a 640gb) can saturate a gigabit network.  no point in an SSD if you are limited by gigabit speeds.

 

AFAIK, there are no known commercially available single decent spinner drive that can saturate a gigabit network. State the drive model and prove me wrong. I know this because its my day job.

 

Now to answer the TS questions.

 

1. Yes. The maximum transfer speed is the slowest speed of both ends (the read speed of source drive and the write speed of target drive) and the maximum channel bandwidth.

2. Theres overhead cost is ripping. If the ripping process is slower than the transfer speed of the ssd, you will get slow speed. I believe, if you want to rip directly to the ssd, then the ssd is underutilize. You also have to consider the slow speed of the blu ray drive.

3. Im not quite up to answer this.

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Not to hijack this thread, but it is kindof relevant.

What is the real world throughput of gigabit?  Using my SSD raid0 (benched at 450MB/s read)  to copy a larege sequential data to a RAM drive I get at best 80MB/s.

To my unraid single spinner i get 70-77MB/s. What i would call saturated gigabit based on my tests.

Now that is using intel nics.

Other nics doing the same test ive only seen 50-60MB/s.

 

So an SDD cache drive is underutilized IMO.

 

Sent from my SGH-I727R using Tapatalk

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WD Caviar Black 640 as a cache drive ... it saturates my gigabit network easily on writes (90-100mb/s per tera copy on 20gb torrents).  Perhaps if I wrote out much more than about 100gb in a given day and started to move towards the slower parts of the drive that would be a different story.  But for sure the first part of the drive is plenty fast enough to not be the bottleneck.

 

So now the question becomes, $/GB ... if you get a 128gb SSD or only use about 128gb of a 640gb spinner ... which is cheaper and which helps you avoid filling up the cache drive.

 

An SSD for cache is wasted over a single gigabit network.  I will ignore your "appeal to authority" logical fallacy. http://www.logicalfallacies.info/relevance/appeals/appeal-to-authority/

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[Nail hit on head] ... Yeah pretty much every test I've seen (hear on Unraid forums and elsewhere on the net) shows a real world max throughput, Ram-to-Ram, at ~110Mb/s ... I have seen over 100 on my network between Win7 and UnRAID (both with Realtek on-board NICs, can't remember the models) through a single Netgear Switch with small frames.

 

FYI: I'm sure you mean 800Mbit ... I never can remember if Mbyte is MB or Mb ... I suppose it is MB but I'll leave my mistake above for posterity :)

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WD Caviar Black 640 as a cache drive ... it saturates my gigabit network easily on writes (90-100mb/s per tera copy on 20gb torrents).  Perhaps if I wrote out much more than about 100gb in a given day and started to move towards the slower parts of the drive that would be a different story.  But for sure the first part of the drive is plenty fast enough to not be the bottleneck.

 

So now the question becomes, $/GB ... if you get a 128gb SSD or only use about 128gb of a 640gb spinner ... which is cheaper and which helps you avoid filling up the cache drive.

 

An SSD for cache is wasted over a single gigabit network.  I will ignore your "appeal to authority" logical fallacy. http://www.logicalfallacies.info/relevance/appeals/appeal-to-authority/

 

Seen on this spec http://www.wdc.com/wdproducts/library/SpecSheet/ENG/2879-701276.pdf, the 2tb wb black hdd is indeed can theoretically saturate the gigabits network. And i was proven wrong. Thanks for the headup.

 

As for ssd, not all ssd can saturate gbits network. seen here are the intel ssd that can saturate the gbits network. lower spec and capacity most likely can not saturate gbits network.

 

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Space is MB, transfer (network) is Mb.  Though nobody can seem to keep them straight and regularly swap their uses and the b/B.

 

800Mb/s = 100MB/s

 

Win 7 and the like with support for larger TCP window sizes as well as using better NIC's and jumbo frames will get you above 800Mb/s sometimes.  Theoretical is close to 900Mb/s or 113MB/s.

 

Keep in mind the actual line usage will be 100%, but 10-20% of that is protocol overheads.

 

 

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WD Caviar Black 640 as a cache drive ... it saturates my gigabit network easily on writes (90-100mb/s per tera copy on 20gb torrents).  Perhaps if I wrote out much more than about 100gb in a given day and started to move towards the slower parts of the drive that would be a different story.  But for sure the first part of the drive is plenty fast enough to not be the bottleneck.

 

So now the question becomes, $/GB ... if you get a 128gb SSD or only use about 128gb of a 640gb spinner ... which is cheaper and which helps you avoid filling up the cache drive.

 

An SSD for cache is wasted over a single gigabit network.  I will ignore your "appeal to authority" logical fallacy. http://www.logicalfallacies.info/relevance/appeals/appeal-to-authority/

 

Seen on this spec http://www.wdc.com/wdproducts/library/SpecSheet/ENG/2879-701276.pdf, the 2tb wb black hdd is indeed can theoretically saturate the gigabits network. And i was proven wrong. Thanks for the headup.

 

As for ssd, not all ssd can saturate gbits network. seen here are the intel ssd that can saturate the gbits network. lower spec and capacity most likely can not saturate gbits network.

 

As for "ignore your "appeal to authority" logical fallacy", i take that as very offensive argument from you, a person who doesnt know how to differentiate between bit and bytes.

 

 

Offensive?  Ironic perhaps, amusing or disingenuous even ... but offensive?  Come on pal ... have a thicker skin.  You made an assertion and then announced, "I know this because its my day job."  Look at my link, that is almost the literal definition of an Appeal to Authority ... and you were wrong.

 

As for my not knowing bits and bytes ... oh have no fear I know those.  Mb vs MB ... yeah I know those too, but I caught myself in a units abbreviation mistake, admitted to it, left it unedited, and then even poked a little fun at myself.

 

As to the actual issue at hand ... it doesn't take a 2TB to saturate a Gb network ... at least not for the first portion of the spinner as I mentioned with my 640GB.  And any SSD that can't saturate a Gb without even breaking a sweat is an SSD not worth the money.

 

Another reason to spend your money on a larger HHD vs an SSD: If you get one the same size as your Parity then it can even act as a spare for a quick swap to limit unprotected downtime.  It will also give you time to shop around for a replacement on-sale.  Important in this time of high HDD prices.

 

I'm curious, exactly what do you consider a saturated Gb network?  Because 125MB/s is the theoretical limit and 111MB/s is the max practical at least according to Tom's Hardware http://www.tomshardware.com/reviews/gigabit-ethernet-bandwidth,2321-7.html.

 

Sooo to answer the OP's questions with facts and not guesses ... an SSD cache is a waste of money and it is limited by the network on writes.  Save the money and get a spinner drive that will still saturate your network for at least half of its capacity and then give your extra "slower" capacity beyond what you'd have gotten with a smaller SSD.  That will even help avoid any problems with the Cache filling up. 

 

FYI, what happens when your cache fills up?  http://lime-technology.com/wiki/index.php?title=Un-Official_UnRAID_Manual#Min._Free_Space  and http://lime-technology.com/forum/index.php?topic=16715.0  If you find yourself in this position, the first solution is to increase mover frequency until you can increase your cache drive size.

 

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WD Caviar Black 640 as a cache drive ... it saturates my gigabit network easily on writes (90-100mb/s per tera copy on 20gb torrents).  Perhaps if I wrote out much more than about 100gb in a given day and started to move towards the slower parts of the drive that would be a different story.  But for sure the first part of the drive is plenty fast enough to not be the bottleneck.

 

So now the question becomes, $/GB ... if you get a 128gb SSD or only use about 128gb of a 640gb spinner ... which is cheaper and which helps you avoid filling up the cache drive.

 

An SSD for cache is wasted over a single gigabit network.  I will ignore your "appeal to authority" logical fallacy. http://www.logicalfallacies.info/relevance/appeals/appeal-to-authority/

 

Seen on this spec http://www.wdc.com/wdproducts/library/SpecSheet/ENG/2879-701276.pdf, the 2tb wb black hdd is indeed can theoretically saturate the gigabits network. And i was proven wrong. Thanks for the headup.

 

As for ssd, not all ssd can saturate gbits network. seen here are the intel ssd that can saturate the gbits network. lower spec and capacity most likely can not saturate gbits network.

 

As for "ignore your "appeal to authority" logical fallacy", i take that as very offensive argument from you, a person who doesnt know how to differentiate between bit and bytes.

 

 

Offensive?  Ironic perhaps, amusing or disingenuous even ... but offensive?  Come on pal ... have a thicker skin.  You made an assertion and then announced, "I know this because its my day job."  Look at my link, that is almost the literal definition of an Appeal to Authority ... and you were wrong.

 

As for my not knowing bits and bytes ... oh have no fear I know those.  Mb vs MB ... yeah I know those too, but I caught myself in a units abbreviation mistake, admitted to it, left it unedited, and then even poked a little fun at myself.

 

As to the actual issue at hand ... it doesn't take a 2TB to saturate a Gb network ... at least not for the first portion of the spinner as I mentioned with my 640GB.  And any SSD that can't saturate a Gb without even breaking a sweat is an SSD not worth the money.

 

Another reason to spend your money on a larger HHD vs an SSD: If you get one the same size as your Parity then it can even act as a spare for a quick swap to limit unprotected downtime.  It will also give you time to shop around for a replacement on-sale.  Important in this time of high HDD prices.

 

I'm curious, exactly what do you consider a saturated Gb network?  Because 125MB/s is the theoretical limit and 111MB/s is the max practical at least according to Tom's Hardware http://www.tomshardware.com/reviews/gigabit-ethernet-bandwidth,2321-7.html.

 

Sooo to answer the OP's questions with facts and not guesses ... an SSD cache is a waste of money and it is limited by the network on writes.  Save the money and get a spinner drive that will still saturate your network for at least half of its capacity and then give your extra "slower" capacity beyond what you'd have gotten with a smaller SSD.  That will even help avoid any problems with the Cache filling up. 

 

FYI, what happens when your cache fills up?  http://lime-technology.com/wiki/index.php?title=Un-Official_UnRAID_Manual#Min._Free_Space  and http://lime-technology.com/forum/index.php?topic=16715.0  If you find yourself in this position, the first solution is to increase mover frequency until you can increase your cache drive size.

 

Thanks guys!

 

I'll pass on a SSD Cache and look into a WD Black when prices come back down. For now I'll use one of my WD EADS drives as a Cache.

 

How about on the PC side.. Would a SSD be any benefit on the PC side of things? Or should I looked into another type of drive?

 

 

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Thanks guys!

 

I'll pass on a SSD Cache and look into a WD Black when prices come back down. For now I'll use one of my WD EADS drives as a Cache.

 

How about on the PC side.. Would a SSD be any benefit on the PC side of things? Or should I looked into another type of drive?

 

given that on the PC side you are generally talking about reads onto the network, that would seem to be an even bigger waste since reads are faster than writes.

 

Now if you are talking about SSD for your PC OS drive well then we are talking about the right thing.  I went SSD on my Win7 machine about a year ago (OCZ Vertex 2 60GB) and on my Laptop (OCZ Vertex 2 50GB) and could not be happier.  Worth every penny.  On the laptop I just deal with not having a lot of space for things like music or movies by using USB / external drives.  But really my usages means I don't need a lot anyway.  For my PC I have a second "data" drive in the form of a 1TB WD Black (was the OS drive prior to the SSD).  Of course that drive used to be about 75% full, but is now only about 20% full since I've moved all media to unraid.  FWIW I keep my important, irreplaceable data on both the PC and UnRaid as well as an external USB because well ... it is unreplacable and yo ucan't have that stuff in too many places.

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FYI, what happens when your cache fills up?  http://lime-technology.com/wiki/index.php?title=Un-Official_UnRAID_Manual#Min._Free_Space  and http://lime-technology.com/forum/index.php?topic=16715.0  If you find yourself in this position, the first solution is to increase mover frequency until you can increase your cache drive size.

 

Be careful of that solution. If you are writing to a platter cache drive while the mover is working then you will get dismal write speeds. I suppose in this case the SSD might show a clear advantage. Better to have a bigger drive than to run the mover more often.

 

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FYI, what happens when your cache fills up?  http://lime-technology.com/wiki/index.php?title=Un-Official_UnRAID_Manual#Min._Free_Space  and http://lime-technology.com/forum/index.php?topic=16715.0  If you find yourself in this position, the first solution is to increase mover frequency until you can increase your cache drive size.

 

Be careful of that solution. If you are writing to a platter cache drive while the mover is working then you will get dismal write speeds. I suppose in this case the SSD might show a clear advantage. Better to have a bigger drive than to run the mover more often.

 

No doubt.  Hence better to have a $100 worth of HDD than $100 worth of SSD for a cache drive.  I'd rather avoid the problem all together than hope that writing to the cache during a mover script isn't too painful on an SSD.

 

But you now make me wonder, our of curiosity, what would happen if I started a big write to cache over the network and then kicked off the mover.  With good NCQ and disk buffers it might not be horrible since the cache drive can read fast and only needs to read as fast as the array is able to write.  So while waiting for the array, the cache can write to itself.  The next question becomes: will the mover script try to process an unfinished file?  Will it skip files that weren't there when it started?  We're getting OT at this point, but the OP did say thanks for the help ;-)

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will the mover script try to process an unfinished file?

it skips actively opened files.

 

Will it skip files that weren't there when it started?

If the particular directory has already been processed, Yes, some files can be skipped until next execution.

 

What if a file opens before the mover and closes before the folder is done being processed?

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WD Caviar Black 640 as a cache drive ... it saturates my gigabit network easily on writes (90-100mb/s per tera copy on 20gb torrents).  Perhaps if I wrote out much more than about 100gb in a given day and started to move towards the slower parts of the drive that would be a different story.  But for sure the first part of the drive is plenty fast enough to not be the bottleneck.

 

So now the question becomes, $/GB ... if you get a 128gb SSD or only use about 128gb of a 640gb spinner ... which is cheaper and which helps you avoid filling up the cache drive.

 

An SSD for cache is wasted over a single gigabit network.  I will ignore your "appeal to authority" logical fallacy. http://www.logicalfallacies.info/relevance/appeals/appeal-to-authority/

 

Seen on this spec http://www.wdc.com/wdproducts/library/SpecSheet/ENG/2879-701276.pdf, the 2tb wb black hdd is indeed can theoretically saturate the gigabits network. And i was proven wrong. Thanks for the headup.

 

As for ssd, not all ssd can saturate gbits network. seen here are the intel ssd that can saturate the gbits network. lower spec and capacity most likely can not saturate gbits network.

 

As for "ignore your "appeal to authority" logical fallacy", i take that as very offensive argument from you, a person who doesnt know how to differentiate between bit and bytes.

 

 

Offensive?  Ironic perhaps, amusing or disingenuous even ... but offensive?  Come on pal ... have a thicker skin.  You made an assertion and then announced, "I know this because its my day job."  Look at my link, that is almost the literal definition of an Appeal to Authority ... and you were wrong.

 

As for my not knowing bits and bytes ... oh have no fear I know those.  Mb vs MB ... yeah I know those too, but I caught myself in a units abbreviation mistake, admitted to it, left it unedited, and then even poked a little fun at myself.

 

As to the actual issue at hand ... it doesn't take a 2TB to saturate a Gb network ... at least not for the first portion of the spinner as I mentioned with my 640GB.  And any SSD that can't saturate a Gb without even breaking a sweat is an SSD not worth the money.

 

Another reason to spend your money on a larger HHD vs an SSD: If you get one the same size as your Parity then it can even act as a spare for a quick swap to limit unprotected downtime.  It will also give you time to shop around for a replacement on-sale.  Important in this time of high HDD prices.

 

I'm curious, exactly what do you consider a saturated Gb network?  Because 125MB/s is the theoretical limit and 111MB/s is the max practical at least according to Tom's Hardware http://www.tomshardware.com/reviews/gigabit-ethernet-bandwidth,2321-7.html.

 

Sooo to answer the OP's questions with facts and not guesses ... an SSD cache is a waste of money and it is limited by the network on writes.  Save the money and get a spinner drive that will still saturate your network for at least half of its capacity and then give your extra "slower" capacity beyond what you'd have gotten with a smaller SSD.  That will even help avoid any problems with the Cache filling up. 

 

FYI, what happens when your cache fills up?  http://lime-technology.com/wiki/index.php?title=Un-Official_UnRAID_Manual#Min._Free_Space  and http://lime-technology.com/forum/index.php?topic=16715.0  If you find yourself in this position, the first solution is to increase mover frequency until you can increase your cache drive size.

 

If you didnt realize, i already edited my post(just as soon as i posted it). Im sorry if i did offend you.

 

And i did learn something from you.

 

;D

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So besides a Cache drive and a WD Black HDD is there anything else I can do to get faster transfer speeds from pc to server?

 

I forgot to answer, but the newest beta has the ability to parallel ethernet runs (can't recall the tech name for this...) enabled so you could run 2 ethernet cables assuming your switch and PC were also capable/set-up.

 

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  • 5 years later...
On 2/28/2012 at 9:39 PM, publicENEMY said:

 

If you didnt realize, i already edited my post(just as soon as i posted it). Im sorry if i did offend you.

 

And i did learn something from you.

 

;D

Lol... wow .. Publicenemy was right.. most drives cant saturate a gigabit network.

 

 

people are always getting MB and Mb confused.

 

--gigbit network 1000Mbps (megabit per sec)

 

DRIVES

--seagate 1.5 (ST31500341AS) can do about 124 Mbps (megabit per sec)

--ssd ~ 450Mbps (megabit per sec)  Samsung 850 Evo 

--m.2 sdd like a Samsung 860 pro 3000Mbps  - if i have another m.2 in a desktop able to transfer,  that connection  would get fully utilized. /(providing i'm not using any QOS).

 

If im copying to  a share and my cache drive is able to pull 300Mbps write , windows copy will show ~37.5 MB (megabyte per sec) 300 / 8 = 37.5   there are 8 bits in a byte.. 

 

and literally speaking there has always been one drive that can saturate a gig network.. (ramdrive) lol the unraid /tmp directory is a ramdrive. if you setup another client on the network with a ramdrive implementation. windows copy should show at least 116MBps (1000mbps / 8). 

 

 

TO truly answer the question

 

as long as your cache drive is faster than the client's drive sending the files

your cache will such those files right it as fast as the write on your SSD can handle.

unless both server and client have drives faster than 1000mb per sec

 

Dont forget windows copy shows transfer rates in MB per sec so times it by 8 to get megabit per sec.

 

 

ps.. marcusone yes at best you're getting 80MB = 640mbps with on a raid 0 (2 x ssd 450mbps) that is just about right. that is what i get.. peaking to 90MB persec.

 

 

Edited by xlordnashx
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8 hours ago, xlordnashx said:

people are always getting MB and Mb confused.

Including yourself

 

8 hours ago, xlordnashx said:

--seagate 1.5 (ST31500341AS) can do about 124 Mbps (megabit per sec)

From the spec sheet, drive can sustain 120MB/s

 

 

8 hours ago, xlordnashx said:

--ssd ~ 450Mbps (megabit per sec)  Samsung 850 Evo 

Up to 520 MB/s

.

.

.

8 hours ago, xlordnashx said:

most drives cant saturate a gigabit network.

I can routinely hit with turbo write enabled 90+ MB/s to hard drives in the array, which for all intents and purposes is close to saturating a 1G network connection

 

8 hours ago, xlordnashx said:

If im copying to  a share and my cache drive is able to pull 300Mbps write , windows copy will show ~37.5 MB (megabyte per sec) 300 / 8 = 37.5   there are 8 bits in a byte.. 

If you enable turbo write, you will see a vast improvement in write speeds (at the expense of all drives being spun up), if there are no other limiting factors

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Pretty impressive dragging up a 5 year old post to rant about another user...

 

Today with the new unRAID, as soon as you use the cache drive for other purposes as well as temporary file storage the SSD has a clear advantage. I've used the cache for years as application storage and never saturated my network with a spinner but can easily do it with the SDD's in there now.

 

The trend to using larger amounts of RAM also has an advantage to write speed unless the file size being transferred is larger then the ram.

 

 

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