Recommended cheap used enterprise sas12 SSD for cachecade?

[funkywizard]

I've noticed the LSI 9300 series (such as 9361-8i or 9361-16i) are the newest that still supports cachecade. The 2gb ram cards support up to a 2TB cache, unlike 512gb max for 1GB hw raid cards.

On 9271 raid cards I just use 4x 400gb Intel DC S3700 drives in raid 10 due to their excellent write endurance, reliability, etc. This gives you the maximum 512gb sized cache, with some space left unused.

As the 9300 series are 12g sas hw raid cards, it made sense to me that you'd ideally want to use sas12 ssds to make the most of the cachecade feature. However, I've not bought any before.

Given the 2TB maximum cache size, and I want to run 4 cache drives in raid 10, a 1tb drive size is ideal. It can be a little bigger, say, up to 1.6tb, or a little smaller, say, 960gb -- If the best drive to get doesn't come as exactly 1tb that's ok. Being able to trust the drive, and the drive coming as close as possible to maxing out the sas12 bus on writes, are the most important criteria.

With that in mind, is there a high endurance (3+ dwpd), low cost, high performance, high reliability equivalent to the DC S3700 in the sas world?

 

[funkywizard]

It looks like the Ultrastar SSD1600MM is a compelling option at 10 DWPD -- any experience with that, or reason to prefer something else?

The specified write speed is ok, not perfect for this use case at a little over 700MB/s -- but acceptable -- assuming it can consistently maintain that write speed.

 

[i386]

I asked a few years ago what's more important for ssd caching (cachecache from broadcom, maxcache from microchip) in hardware raid: bandwidth (MByte/s) or IOPS.
For maxcache IOPS are more important because only io requests up to 64KByte are cached on the ssds, larger io goes directly to the raid volume.

It looks like the Ultrastar SSD1600MM is a compelling option at 10 DWPD -- any experience with that, or reason to prefer something else?

I have HUSMM8020ASS200 and I love them, great devices. Two of them of them have each over 120 TBytes written to them and still perform like brand new devices

 

[funkywizard]

I asked a few years ago what's more important for ssd caching (cachecache from broadcom, maxcache from microchip) in hardware raid: bandwidth (MByte/s) or IOPS.
For maxcache IOPS are more important because only io requests up to 64KByte are cached on the ssds, larger io goes directly to the raid volume.

I have HUSMM8020ASS200 and I love them, great devices. Two of them of them have each over 120 TBytes written to them and still perform like brand new devices

Right, that makes sense. I wonder how cachecade handles it.

I can see the point -- if a write request comes in that's a full raid stripe or larger, may as well just write it to the hard drives since they do their best work for large sequential transfers anyway. Typically any sequential transfer of 128KB or more will allow you to get nearly the full sequential speed out of a spinning disk. You still get benefit of the raid card ram cache in those cases where the initial write skips the SSD cache.

Older SSDs (like the ones available when these caching routines were developed) were not very good at sequential write. Also, endurance (in terms of total terabytes written before failure) was more of a concern on older smaller drives than modern larger drives. So back then, it would have been a really bad idea to use the SSD array as a writeback cache for large sequential writes.

These days its more of a toss up. If you're writing large sequential i/o to the cache pool, high odds you'll just have to read that data again and flush it out of the cache before long. Constantly churning the cache pool would use up a lot of the available performance of the cache device so it wouldn't have as much storage or bandwidth available to service (potential) cache hits.

 

[JoshDi]

I run cachecade on my 9285 LSI card. Cachecade really helps with IO and random read/write. It was originally created for MySQL databases.

I run 2x raid6 arrays with cachecade on top and bcache on top of that. Bcache is definitely a larger impact than cachecade. Overall though,sustained sequential writes/reads wont benefit from either cachecade or bcache because they will bypass the cache.