cache drive question

[ratmice]

I'm not sure exactly where to post this, so please move if there's a better location.

 

Is there any formula (loosely speaking) for figuring out the best size for a cache drive, what slot to place it in (MoBo, or controller), type of drive (fast, slow, SSD etc...).

[jamerson9]

1. Size : greater than the amount of files you want to transfer before the mover script moves it to the array.

2. Slot : depends on what type of add-on controller, motherboard bus support, number of disks and disk activity, but, in general motherboard.

3. Speed : faster the better, only constrained by your personal (or spousal) threshold on hardware spending.

[Rajahal]

I agree with the above.  The only thing I'll add is that a cache drive should not be placed on a Supermicro AOC-SASLP-MV8 card.  I don't remember the exact details as to why, bit it was something about an immature drive that caused the drive to spin up and down constantly.  The motherboard is always the safest choice.

 

SSDs can make nice cache drives (low power consumption, no spin up lag, slightly faster than 7200rpm drives, etc.), but be aware that they have a hard limit on the number of writes they can withstand.  So if you use an SSD as a cache drive and write to the array regularly, be prepared to replace it after a year or two of regular use.  Also don't use the cache drive for any mission critical data as you never know when it may die on you...though the same is true of any drive used as a cache drive.

[Ulvan]

SSDs can make nice cache drives (low power consumption, no spin up lag, slightly faster than 7200rpm drives, etc.), but be aware that they have a hard limit on the number of writes they can withstand.  So if you use an SSD as a cache drive and write to the array regularly, be prepared to replace it after a year or two of regular use.

 

This is largely FUD when we're talking modern SSDs, and certainly 1-2 replacement cycle is not necessary even in the most demanding home environments. I'd be much more concerned about garbage collection, but that's also mostly a solved issue with recent controllers and firmware.

[jakebake]

I'm looking to get a cache drive. Not ssd too expensive right now, but I do want it to be fast. Are the western digital blues fast enough? Also I know it is recommended to get a 2tb (since my other drives are) so it can be a warm spare, but I think I'd rather get a 250-500gb drive now for cache and just buy a spare drive later.

 

Can you guys recommend me a good fast drive (not too expensive) and also how many of you are actually using a big cache drive for a warm spare or just have a smaller cache.

 

I was looking at this: http://www.newegg.com/Product/Product.aspx?Item=N82E16822136073&cm_re=western_digital_caviar_blue-_-22-136-073-_-Product

[dgaschk]

I use a 2TB Seagate drive as a cache. I initially meant it as a warm spare, but since I been building more servers I seem to always a spare around anyway. I don't delete the original files for at least 24 hours so I can be sure that the data has been moved into the array.