Secure Erase is currently a entire drive function, its writes all the cell resetting it. It also updates the firmware GC maps so it knows the drive is clean. Trim just gives more info the firmware that a block is unused (as normally a delete is just updating an index table and the firmware has no way of knowing which cells are no longer needed by the OS).
Currently firmware is meant to help conventional file system usage. However ZIL isn't normal usage and as such *IF* and it's a big if, we can effectively bypass the firmware trying to be clever or at least help it be clever then we can avoid the downgrade over time. In particular if we could secure erase a few cells as once as required, the lifetime would be much longer, I'd even argue that taking the wear leveling off the drives hand would be useful in the ZIL case. The other thing is the slow down only occurs once the SSD fills and has to start getting clever where to put things and which cells to change, for a ZIL that is again something we could avoid in software fairly easy. Its also worth putting this in perspective, a complete secure erase every night to restore performance to your ZIL would still let the SSD last for *years*. And given how cheap some SSD are, it is probably still cheaper to effectively burn the ZIL out and just replace it once a year. Maybe not a classic level of RAID but the very essence of the idea, lots of cheap can be better than expensive if you know what you are doing. Bye, Deano -----Original Message----- From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss-boun...@opensolaris.org] On Behalf Of Christopher George Sent: 23 December 2010 16:46 To: zfs-discuss@opensolaris.org Subject: Re: [zfs-discuss] Looking for 3.5" SSD for ZIL > However, this *can* be overcome by frequently re-formatting the SSD (not > the Solaris format, a low-level format using a vendor-supplied utility). For those looking to "Secure Erase" a OCZ SandForce based SSD to reclaim performance, the following OCZ Forum thread might be of interest: http://www.ocztechnologyforum.com/forum/showthread.php?75773-Secure-Erase-TR IM-and-anything-else-Sandforce OCZ uses the term "DuraClass" as a catch-all for algorithms controlling wear leveling, drive longevity... There is a direct correlation between Secure Erase frequency and expected SSD lifetime. Thread #1 detailing a recommended frequency of Secure Erase use: "3) Secure erase a drive every 6 months to free up previously read only blocks, secure erase every 2 days to get round Duraclass and you will kill the drive very quickly" Thread #5 explaining DuraClass and relationship to TRIM: "Duraclass is limiting the speed of the drive NOT TRIM. TRIM is used along with wear levelling." Thread #6 provides more details of DuraClass and TRIM: "Now Duraclass monitors all writes and control's encryption and compression, this is what effects the speed of the blocks being written to..NOT the fact they have been TRIM'd or not TRIM'd." "You guys have become fixated at TRIM not speeding up the drive and forget that Duraclass controls all writes incurred by the drive once a GC map has been written." Above excerpts written by a OCZ employed thread moderator (Tony). Best regards, Christopher George Founder/CTO www.ddrdrive.com -- This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
