From mboxrd@z Thu Jan 1 00:00:00 1970 From: Martin Subject: btrfs on low end and high end FLASH Date: Wed, 02 May 2012 00:18:32 +0100 Message-ID: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 To: linux-btrfs@vger.kernel.org Return-path: List-ID: How well suited is btrfs to low-end and high-end FLASH devices? Paraphrasing from a thread elsewhere: FLASH can be categorised into two classes, which have extremely different characteristics: (a) the low-end (USB, SDHC, CF, cheap ATA SSD); and (b) the high-end (SAS, PCIe, NAS, expensive ATA SSD). My own experience is that the low end (a) can have erase blocks as large as 4MBytes or more and they are easily worn out to failure. I've no idea what their page sizes might be nor what boundaries their wear levelling (if any) operate on. Their normal mode of operation is to use a "FAT32" filesystem and to be filled up linearly with large files. I guess the more scattered layout of extN is non-too sympathetic to their normal operation. The high-end (b) may well have 4kByte pages or smaller but they will typically operate with multiple page chunks that are much larger, where 16kBytes appear to be the optimum performance size for the devices I've seen so far. How well does btrfs fit in with the features for those two categories? Regards, Martin