iSRT and TRIM

[sabzingeur]

Does Z68 iSRT support TRIM?

Basically, intel RAID did not support TRIM until they released a driver that support TRIM in RAID 0 and 1, but not RAID 5.

iSRT is an SSD doing caching in a RAID configuration with a HDD. What kind of RAID is this configuration similar to? And is TRIM supported?

Because without TRIM and the extensive that nature of caching, speed will soon decrease to a very low level.

 

[gjs278]

Because without TRIM and the extensive that nature of caching, speed will soon decrease to a very low level.

even without trim, the speed of your drive would be nearly the same at all levels. the drive is overprovisioned and has garbage collection. the speed difference on ssds as well is very similar for 25%, 50%, and even 75% full. that said, I do not know if trim works, but I do know that I wouldn't worry about it.

if you buy an slc drive, you don't even need the trim, because the cells can write at a similar speed full or empty. grab the 311 and use that.

 

[omniscence]

As far as I know TRIM is still not supported in RAID configurations. Intel stated that they used improper wording in their first press release. What does work now is TRIM while the controller is in RAID mode for drives that are just passed through alongside a RAID. Former drivers did not allow TRIM at all while in RAID mode, so you had to use a separate controller if you wanted TRIM on a plain SSD alongside a HDD-RAID.

On the other hand I doubt that you would get much use from TRIM for SSD completely used for caching. That SSD should be filled nearly 100% most of the time, and SRT is most probably not going to erase data without overwriting it immediately. So there is no free space within the usable area of the drive. There is nothing to be TRIMmed on a full drive.

What could be of use is TRIM on the remaining part of an SSD where only a part is used for SRT. SDDs in SRT-mode are currently represented as RAID0 by the driver, so I think TRIM does not work at all for these SSDs.

 

[sabzingeur]

The question is, must I use an SLC drive for caching, since, without TRIM, i suppose a MLC cache drive will slow down dramatically once it's full?

 

[omniscence]

You can still overprovision that drive, i.e. only use 50 GB of an 64 GB drive. I just throwing around some arbitrary numbers, not sure that these are optimal.

 

[gjs278]

The question is, must I use an SLC drive for caching, since, without TRIM, i suppose a MLC cache drive will slow down dramatically once it's full?

no and not really. drives at 50% perform just as bad as drives 75% full. also, they overprovision the drives manually for you, so a drive is never truly 100% full, there are always spared reserved gbs of space.

http://www.hardocp.com/article/2011/08/07/nand_flash_faces_off_synchronous_vs_asynchronous/4

check out the difference between a 50% drive and 75% in the benchmark. it's like nothing at all.

http://www.anandtech.com/show/4337/z68-ssd-caching-with-corsairs-f40-sandforce-ssd/4

there's a comparison charts of drives. if you want a 311 to ease your mind, it's about $115 for 20gb, and it's slc. if you want a bigger size (which you probably will not need), then check out that list, find a drive with good write speed, and have at it.

 

[sabzingeur]

You can still overprovision that drive, i.e. only use 50 GB of an 64 GB drive. I just throwing around some arbitrary numbers, not sure that these are optimal.

no and not really. drives at 50% perform just as bad as drives 75% full. also, they overprovision the drives manually for you, so a drive is never truly 100% full, there are always spared reserved gbs of space.

But as it is a cache drive, it is supposed to be full most of the time, isn't it? And that means every time these is a write operation, a full block of data must be read into memory, modified, and overwritten, which slows down the SSD. As explained here:
http://www.anandtech.com/show/2738/8

While an SLC drive means no speed reduction?

 

[gjs278]

But as it is a cache drive, it is supposed to be full most of the time, isn't it? And that means every time these is a write operation, a full block of data must be read into memory, modified, and overwritten, which slows down the SSD. As explained here:
http://www.anandtech.com/show/2738/8

yes, but reference the chart above. at 25% full and 75% full, there is only a 10% difference in performance. the performance loss is not as great as you can expect, and drive manufacturers always put more flash on the drive than is actually used. anytime you purchase say a 40gb drive, you are actually buying a 44gb drive where they reserve 4gb of it as an overprovision to make sure the drive doesn't slowdown when 40gb of space is in use.

I do not know exactly what impact slc has on drives that are filled compared to mlc drives, but I do know intel made that 311 specifically for z68 caching, and they made it slc for what I can gather is just improved write performance and wear time, not necessary performance when the drive is full.