klinetobewa
1 Copper

RE: PowerEdge SSD RAID Options

Josh,

I'm not so sure this is the verified answer. I followed the link you provided and from that page linked to a white paper about Dell SSD FAQ. In this white paper it said Dell Drives don't currently support TRIM. So even if the controller did it would be useless. This paper looks to be old. Can you point us to something more current? I have a ton of questions and documentation is really lacking. How much the drives are over provisioned from factory (%) ? What RAID levels support passing the TRIM/UNMAP commands? Does it work with all RAID levels supported by the controller, or it it only RAID-1 and RAID-0? Or is the TRIM only supported in Non-RAID (pass-through)? What OS is this certified for or is it any OS that can send TRIM commands?

http://i.dell.com/sites/doccontent/shared-content/data-sheets/Documents/Solid-State-Drive-FAQ-us.pdf

14. What is TRIM/UNMAP and do Dell enterprise SSD drives support it? Certain Operating Systems support the TRIM function, which translates deleted files to the associated LBA (logical block address) on the storage device (SSD). For SATA, the command is also called TRIM, for SAS, the command is called UNMAP. The TRIM/UNMAP command notifies the drive it no longer needs data in certain LBAs (Logical Block Address) which then free up a number of NAND pages. The TRIM/UNMAP command needs to be supported by the OS, the drive, and the controller in order to work. The TRIM/UNMAP command could result in higher SSD performance from both the reduced data needed to be rewritten during garbage collection and the higher free space resulting on the drive. Current shipping Dell enterprise drives have high enough performance and endurance so they do not yet support these commands even if the OS supports them. These features are being investigated for subsequent Dell SSD offerings.

Also, there is no mention of TRIM support from LSI, which the PERC H730, and H730P are based on.

http://www.lsi.com/downloads/Secure/RAID%20Sales%20Tools/SAS%20ROC/LSISAS3108%20product%20brief.pdf

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klinetobewa
1 Copper

RE: PowerEdge SSD RAID Options

Can you link to this white paper you speak of. I cannot find much at all about SSD and RAID Support from Dell or online.

"I have seen on these forums that this or similar configurations are supported and even saw a whitepaper on Dell's website where a 4-disk SSD RAID 10 was used, but yet my assigned SE just told me that SSD drives in a RAID configuration is not "recommended" by Dell and is instead trying to sell me the SanDisk DAS Cache solution."

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klinetobewa
1 Copper

RE: PowerEdge SSD RAID Options

Did your configuration work? Let me define work, did you get TRIM support? 

I'm only asking because I had another engineer friend of mine do a configuration and within a month his server was ground to a halt at 30/MB/s or about the speed of a USB thumb drive.

RAID configurations are becoming more important/possible with the cheaper MLC SATA SSD so I'm hoping for this to be a possibility now. From what I'm seeing online I'm not seeing this work for most people. I'm also hearing a lot of what I consider to be misinformation about not needing TRIM because the GC is so good on controllers now. 

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klinetobewa
1 Copper

RE: RAID 1 support on Dell PowerEdge R730 with Perc H730 and SSD disks

Arjan,

I'm not so sure this is the verified answer. I followed the link you provided and from that page linked to a white paper about Dell SSD FAQ. In this white paper it said Dell Drives don't currently support TRIM. So even if the controller did it would be useless. This paper looks to be old. Can you point us to something more current? I have a ton of questions and documentation is really lacking. How much the drives are over provisioned from factory (%) ? What RAID levels support passing the TRIM/UNMAP commands? Does it work with all RAID levels supported by the controller, or it it only RAID-1 and RAID-0? Or is the TRIM only supported in Non-RAID (pass-through)? What OS is this certified for or is it any OS that can send TRIM commands?

i.dell.com/.../Solid-State-Drive-FAQ-us.pdf

14. What is TRIM/UNMAP and do Dell enterprise SSD drives support it? Certain Operating Systems support the TRIM function, which translates deleted files to the associated LBA (logical block address) on the storage device (SSD). For SATA, the command is also called TRIM, for SAS, the command is called UNMAP. The TRIM/UNMAP command notifies the drive it no longer needs data in certain LBAs (Logical Block Address) which then free up a number of NAND pages. The TRIM/UNMAP command needs to be supported by the OS, the drive, and the controller in order to work. The TRIM/UNMAP command could result in higher SSD performance from both the reduced data needed to be rewritten during garbage collection and the higher free space resulting on the drive. Current shipping Dell enterprise drives have high enough performance and endurance so they do not yet support these commands even if the OS supports them. These features are being investigated for subsequent Dell SSD offerings.

Also, there is no mention of TRIM support from LSI, which the PERC H730, and H730P are based on.

What about using them in a RAID-6, RAID-10, RAID-50?

The documentation just says: "Support for TRIM/UNMAP Commands for SAS/SATA SSDs"

That is either a blanket statement that means it works on all RAID configurations or extremely vague and I'm willing to bet there are some details missing. 

Can you point us to some white papers, confirmed configurations, or other documentation?

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klinetobewa
1 Copper

RE: Server SSDs in RAID 1: Software or Hardware RAID

I would have to say that you do need TRIM. You can live without it, but your SSD won't perform the best it could. 

arstechnica.com/.../ask-ars-my-ssd-does-garbage-collection-so-i-dont-need-trim-right

"There is a barrier between the world of files and the world of blocks. The operating system doesn’t have any say in how an SSD’s controller does its job or which blocks the SSD controller uses to write data—the OS knows all about its file system, but nothing about the blocks underneath. Similarly, the SSD’s controller knows everything about what blocks are in use and what blocks are free, but it has no way of knowing which blocks correspond to which files."

"With TRIM, an SSD is no longer forced to save pages belonging to deleted files. TRIM doesn’t obviate the need for garbage collection—it works with garbage collection to more properly mark pages as stale. And you don’t need TRIM for garbage collection to work—but TRIM makes an SSD’s garbage collection more efficient."

This statement seems misleading in your post:

"When you use a chipset/driver based RAID controller or a hardware controller then TRIM is not necessary. If the controller supports SSDs then it has some method to let the drive know the block is unused. The operating system does not have direct communication with the drive, so the RAID controller handles that type of operation."

What is this magical "some method" you speak of? 

There are lots of questions about this online. It seems a lot of folks want TRIM on their RAID....lmgtfy.com

More resources about TRIM an Garbage Collection: https://www.cindori.org/trim-vs-garbage-collection/

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klinetobewa
1 Copper

RE: RAID SSD config recommendation

Geoff,

Looking for a verified answer. I followed the link to a white paper about Dell SSD FAQ. In this white paper it said Dell Drives don't currently support TRIM. So even if the controller did it would be useless. This paper looks to be old. Can you point us to something more current? I have a ton of questions and documentation is really lacking. How much the drives are over provisioned from factory (%) ? What RAID levels support passing the TRIM/UNMAP commands? Does it work with all RAID levels supported by the controller, or it it only RAID-1 and RAID-0? Or is the TRIM only supported in Non-RAID (pass-through)? What OS is this certified for or is it any OS that can send TRIM commands?

i.dell.com/.../Solid-State-Drive-FAQ-us.pdf

14. What is TRIM/UNMAP and do Dell enterprise SSD drives support it? Certain Operating Systems support the TRIM function, which translates deleted files to the associated LBA (logical block address) on the storage device (SSD). For SATA, the command is also called TRIM, for SAS, the command is called UNMAP. The TRIM/UNMAP command notifies the drive it no longer needs data in certain LBAs (Logical Block Address) which then free up a number of NAND pages. The TRIM/UNMAP command needs to be supported by the OS, the drive, and the controller in order to work. The TRIM/UNMAP command could result in higher SSD performance from both the reduced data needed to be rewritten during garbage collection and the higher free space resulting on the drive. Current shipping Dell enterprise drives have high enough performance and endurance so they do not yet support these commands even if the OS supports them. These features are being investigated for subsequent Dell SSD offerings.

Also, there is no mention of TRIM support from LSI, which the PERC H730, and H730P are based on.

What about using them in a RAID-6, RAID-10, RAID-50?

The documentation just says: "Support for TRIM/UNMAP Commands for SAS/SATA SSDs"

That is either a blanket statement that means it works on all RAID configurations or extremely vague and I'm willing to bet there are some details missing. 

Can you point us to some white papers, confirmed configurations, or other documentation?

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